Catalyst system for preparing propylene oxide

ABSTRACT

A catalytic system containing a titanium zeolite of structure type MWW optionally containing zinc and containing at least one of an inorganic potassium salt and an organic potassium salt is provided. The catalyst system is useful in the preparation of propylene oxide.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of prior U.S. applicationSer. No. 14/908,042, filed Jan. 27, 2016, the disclosure of which isincorporated herein by reference in its entirety. U.S. application Ser.No. 14/908,042 is the National Stage of PCT/EP2014/065239, filed Jul.16, 2014, the disclosure of which is incorporated herein by reference inits entirety. U.S. application Ser. No. 14/908,042 claims priority toEuropean Application No. 13177905.0, filed Jul. 24, 2013, the disclosureof which is incorporated herein by reference in its entirety.

The present invention relates to a continuous process for thepreparation of propylene oxide wherein a titanium zeolite of frameworkstructure type MWW optionally comprising zinc is employed as epoxidationcatalyst and wherein in the liquid feed stream passed into theepoxidation reactor, at least one dissolved potassium salt is present.

Propylene oxide is an important intermediate in the chemical industry. Asuitable process for the preparation of propylene oxide starts frompropene and makes use of hydrogen peroxide as oxidizing agent,acetonitrile as solvent and a heterogeneous zeolitic epoxidationcatalyst having MWW framework structure and containing titanium.Reference is made, for example, to WO 2011/006990. Due to its importancefor industrial-scale processes, it is desired to carry out thisepoxidation reaction as efficiently as possible. Therefore, theconversion rates of the starting materials and the selectivity topropylene oxide should be as high as possible.

For a specific case where hydrogen peroxide is produced in situ in theepoxidation reactor, WO 20091008493 teaches that an ammonium salt shouldbe present in the reactor. As conceivable salts, ammonium carbonate,ammonium hydrogen carbonate, ammonium dihydrogen phosphate, ammoniumhydrogen phosphate, ammonium phosphate, ammonium hydrogen pyrophosphate,ammonium pyrophosphate, ammonium chloride, ammonium nitrate and ammoniumacetate are disclosed. As preferred salts, ammonium dihydrogenphosphate, ammonium hydrogen phosphate, and ammonium phosphate arementioned. According to the examples of WO 2009/008493 where hydrogenperoxide is formed in situ from hydrogen and oxygen as startingmaterials and where, accordingly, a noble metal catalyst is employed incombination with a titanium containing zeolite catalyst of structuretype MWW, ammonium dihydrogen phosphate is used. A theoretical exampleof WO 2009/008493 where hydrogen peroxide is employed as such and wherea titanium containing zeolite catalyst of structure type MWW is employedwithout an additional noble metal catalyst, no ammonium salt is added.

WO 2011/006990, cited above, teaches in the example the use of ammoniumdihydrogen phosphate.

WO 2012/074118 and WO 2011/152268 relate to methods for producing anolefin oxide comprising reacting hydrogen peroxide with an olefin in thepresence of a titanosilicate. Both documents disclose that buffers maybe added, wherein numerous cations and anions are listed which may servefor forming a buffer. In both documents, ammonium dihydrogen phosphateand diammonium hydrogen phosphate, respectively, are preferred as abuffer.

WO 2012/157473 relates to a method for producing atitanosilicate-containing catalyst and its use in an epoxidationreaction of an olefin with hydrogen peroxide. A buffering agent may beadded, wherein the specific examples of preferred buffering agents areammonium salts, wherein ammonium benzoate, ammonium dihydrogen phosphateand diammonium hydrogen phosphate are preferred.

Xiangqing Fang et al., Phys. Chem. Chem. Phys. 2013, 15, 4930-4938relates to a titanosilicate of the MWW type in which fluorine specieshave been implanted by post-treatment.

U.S. 2010/0234623 relates to a method for producing propylene oxide inthe presence of a supported gold cluster catalyst.

Lihao Tang et al., Macromolecules, 2008, 41, 7306-7315 disclosescatalysts for the ring-opening polymerization of ethylene oxide andpropylene oxide based on products of alkylammonium compounds with bulkytetraphenol ligands.

It was an object of the present invention to provide an improvedcontinuous process for the epoxidation of propene with hydrogen peroxideas oxidizing agent in the presence of a catalyst containing a titaniumzeolite of framework structure type MWW and in the presence ofacetonitrile as solvent.

It was a further object of the present invention to provide a catalyticsystem which exhibits an excellent long-time stability, in particular interms of propylene oxide selectivity and hydrogen peroxide conversion.

Surprisingly, it was found that these objects can be solved if in thecontinuous reaction, a titanium zeolite of framework structure type MWWis employed as epoxidation catalyst and a liquid feed stream to be fedinto the epoxidation reactor is provided which comprises propene,hydrogen peroxide, acetonitrile, water, and at least one dissolvedpotassium salt.

Therefore, the present invention relates to a continuous process for thepreparation of propylene oxide, comprising

-   (i) providing a liquid feed stream comprising propene, hydrogen    peroxide, acetonitrile, water, optionally propane, and at least one    dissolved potassium salt;-   (ii) passing the feed stream provided in (i) into an epoxidation    reactor comprising a catalyst comprising a titanium zeolite of    structure type MWW, and subjecting the feed stream to epoxidation    reaction conditions in the epoxidation reactor, obtaining a reaction    mixture comprising propylene oxide, acetonitrile, water, the at    least one potassium salt, optionally propene, and optionally    propane;-   (iii) removing an effluent stream from the epoxidation reactor, the    effluent stream comprising propylene oxide, acetonitrile, water, at    least a portion of the at least one potassium salt, optionally    propene, and optionally propane.

Further, the present invention relates to a catalytic system comprisinga catalyst comprising a titanium zeolite of structure type MWWoptionally comprising zinc, and at least one potassium salt, wherein theat least one potassium salt is selected from the group consisting of atleast one inorganic potassium salt, at least one organic potassium salt,and combinations of at least one inorganic potassium salt and at leastone organic potassium salt.

Step (i)

Surprisingly, it was found that the presence of at least one dissolvedpotassium salt in the liquid feed stream provided in (i) allows for anexcellent epoxidation performance of the epoxidation catalyst employedin (ii) which comprises the titanium zeolite of framework structure typeMWW, in contrast to the prior art which recommends ammonium dihydrogenphosphate as additive. Yet further, it was surprisingly found that whilethe corresponding potassium salt, potassium dihydrogen phosphate, is byfar the better additive, the epoxidation characteristics in terms ofhydrogen peroxide conversion and propylene oxide selectivty can still beimproved if organic potassium salts are used as additives.

Regarding the chemical nature of the at least one potassium salt isconcerned, no specific restrictions exist. Preferably, the at least onepotassium salt is selected from the group consisting of at least oneinorganic potassium salt, at least one organic potassium salt, andcombinations of at least one inorganic potassium salt and at least oneorganic potassium salt.

Preferred inorganic potassium salts include, but are not restricted to,potassium halides such as potassium chloride or potassium bromide,potassium nitrate, potassium sulfate, potassium hydrogen sulfate,potassium hydroxide, potassium perchlorate, potassium salts comprisingphosphorus such as potassium dihydrogen phosphate or dipotassiumhydrogen phosphate or potassium phosphate or potassium pyrophosphatessuch as monobasic potassium pyrophosphate or dibasic potassiumpyrophosphate or tribasic potassium pyrophosphate or tetrabasicpotassium pyrophosphate, or potassium etidronates such as monobasicpotassium etidronate or dibasic potassium etidronate or tribasicpotassium etidronate or tetrabasic potassium etidronate, potassiumcyanate, potassium oxides such as potassium oxide (K₂O) or potassiumsuperoxide (KO₂) or potassium peroxide (K₂O₂). Preferably, the inorganicpotassium salt is selected from the group consisting of potassiumhydroxide, potassium halides, potassium nitrate, potassium sulfate,potassium hydrogen sulfate, potassium perchlorate, and a combination oftwo or more thereof.

Preferred organic potassium salts include, but are not restricted to,potassium carbonate (K₂CO₃), potassium hydrogen carbonate, potassiumsalts of aliphatic saturated carboxylic acids such as monocarboxylicacids preferably having from 1 to 6, more preferably from 1 to 5, morepreferably from 1 to 4, more preferably from 1 to 3 carbon atoms such asformic acid, acetic acid, propionic acid, dicarboxylic acids preferablyhaving from 2 to 6, more preferably from 2 to 4 carbon atoms such asoxalic acid, malonic acid, succinic acid, tartaric acid, tricarboxylicacids preferably having from 6 to 10 carbon atoms such as citric acid orisocitric acid or propane-1,2,3-tricarboxylic acid, or tetracarboxylicacids. Preferably, the organic potassium salt is selected from the groupconsisting of potassium salts of aliphatic saturated monocarboxylicacids preferably having 1, 2, 3, 4, 5 or 6 carbon atoms, potassiumcarbonate, and potassium hydrogen carbonate. More preferably, theorganic potassium salt is selected from the group consisting ofpotassium formate, potassium acetate, potassium propionate, potassiumcarbonate, and potassium hydrogen carbonate. More preferably, theorganic potassium salt is selected from the group consisting ofpotassium formate, potassium acetate, potassium carbonate, and potassiumhydrogen carbonate.

Therefore, the at least one potassium salt is preferably selected fromthe group consisting of at least one inorganic potassium salt selectedfrom the group consisting of potassium hydroxide, potassium halides,potassium nitrate, potassium sulfate, potassium hydrogen sulfate,potassium perchlorate, at least one organic potassium salt selected fromthe group consisting of potassium salts of aliphatic saturatedmonocarboxylic acids preferably having 1, 2, 3, 4, 5 or 6 carbon atoms,potassium carbonate, and potassium hydrogen carbonate, and a combinationof at least one of the at least one inorganic potassium salts and atleast one of the at least one organic potassium salts.

More preferably, the at least one potassium salt is selected from thegroup consisting of at least one inorganic potassium salt selected fromthe group consisting of potassium hydroxide, potassium halides,potassium nitrate, potassium sulfate, potassium hydrogen sulfate,potassium perchlorate, at least one organic potassium salt selected fromthe group consisting of potassium formate, potassium acetate, potassiumpropionate, potassium carbonate, and potassium hydrogen carbonate, and acombination of at least one of the at least one inorganic potassiumsalts and at least one of the at least one organic potassium salts.

More preferably, the at least one potassium salt is selected from thegroup consisting of at least one inorganic potassium salt selected fromthe group consisting of potassium hydroxide, potassium chloride,potassium nitrate, at least one organic potassium salt selected from thegroup consisting of potassium formate, potassium acetate, potassiumcarbonate, and potassium hydrogen carbonate, and a combination of atleast one of the at least one inorganic potassium salts and at least oneof the at least one organic potassium salts.

Preferably, at least one of the at least one potassium salt according to(i) is an organic potassium salt. Therefore, if according to (i), onesingle potassium salt is employed, the potassium salt is preferably anorganic potassium salt, more preferably selected from the groupconsisting of potassium salts of aliphatic saturated monocarboxylicacids preferably having 1, 2, 3, 4, 5 or 6 carbon atoms, potassiumcarbonate, and potassium hydrogen carbonate, more preferably selectedfrom the group consisting of potassium formate, potassium acetate,potassium propionate, potassium carbonate, and potassium hydrogencarbonate, more preferably selected from the group consisting ofpotassium formate, potassium acetate, potassium carbonate, and potassiumhydrogen carbonate. If according to (i) two or more potassium salts areemployed, at least one potassium salt is preferably an organic potassiumsalt, more preferably selected from the group consisting of potassiumsalts of aliphatic saturated monocarboxylic acids preferably having 1,2, 3, 4, 5 or 6 carbon atoms, potassium carbonate, and potassiumhydrogen carbonate, more preferably selected from the group consistingof potassium formate, potassium acetate, potassium propionate, potassiumcarbonate, and potassium hydrogen carbonate, more preferably selectedfrom the group consisting of potassium formate, potassium acetate,potassium carbonate, and potassium hydrogen carbonate.

Especially preferably, one of the at least one potassium salt accordingto (i) is potassium formate, potassium acetate, or a mixture thereof,preferably potassium formate. Therefore, if according to (i), one singlepotassium salt is employed, the potassium salt is most preferablypotassium formate or potassium acetate, preferably potassium formate. Ifaccording to (i) two or more potassium salts are employed, one potassiumsalt is potassium formate, potassium acetate, or a mixture thereof,preferably potassium formate.

According to an embodiment of the present invention, in case one singlepotassium salt is employed according to (i) as the at least onepotassium salt, the potassium salt is not potassium dihydrogenphosphate. According to an embodiment of the present invention, in caseone single potassium salt is employed according to (i) as the at leastone potassium salt, the potassium salt is not a potassium salt of aphosphorus oxyacid wherein the molar ratio of potassium relative tophosphorus in the potassium salt of the at least one phosphorus oxyacidis in the range of from 0.6 to 1.4. According to an embodiment of thepresent invention, in case one single potassium salt is employedaccording to (i) as the at least one potassium salt, the potassium saltis not dipotassium hydrogen phosphate. According to an embodiment of thepresent invention, in case one single potassium salt is employedaccording to (i) as the at least one potassium salt, the potassium saltis neither potassium dihydrogen phosphate nor a potassium salt of aphosphorus oxyacid wherein the molar ratio of potassium relative tophosphorus in the potassium salt of the at least one phosphorus oxyacidis in the range of from 0.6 to 1.4. According to an embodiment of thepresent invention, in case one single potassium salt is employedaccording to (i) as the at least one potassium salt, the potassium saltis neither potassium dihydrogen phosphate nor a potassium salt of aphosphorus oxyacid wherein the molar ratio of potassium relative tophosphorus in the potassium salt of the at least one phosphorus oxyacidis in the range of from 0.6 to 1.4 nor dipotassium hydrogen phosphate.

Therefore, the present invention especially preferably relates to acontinuous process for the preparation of propylene oxide, comprising

-   (i) providing a liquid feed stream comprising propene, hydrogen    peroxide, acetonitrile, water, optionally propane, and dissolved    potassium formate, potassium acetate, or a mixture thereof,    preferably potassium formate;-   (ii) passing the feed stream provided in (i) into an epoxidation    reactor comprising a catalyst comprising a titanium zeolite of    structure type MWW, and subjecting the feed stream to epoxidation    reaction conditions in the epoxidation reactor, obtaining a reaction    mixture comprising propylene oxide, acetonitrile, water, the    potassium formate, potassium acetate, or a mixture thereof,    preferably the potassium formate, optionally propene, and optionally    propane;-   (iii) removing an effluent stream from the epoxidation reactor, the    effluent stream comprising propylene oxide, acetonitrile, water, at    least a portion of the potassium formate, potassium acetate, or a    mixture thereof, preferably of the potassium formate, optionally    propene, and optionally propane.

According to an embodiment of the present invention, the at least onepotassium salt according to (i) does not comprise potassium dihydrogenphosphate. According to an embodiment of the present invention, the atleast one potassium salt does not comprise a potassium salt of aphosphorus oxyacid wherein the molar ratio of potassium relative tophosphorus in the potassium salt of the at least one phosphorus oxyacidis in the range of from 0.6 to 1.4. According to an embodiment of thepresent invention, the at least one potassium salt according to (i) doesnot comprise dipotassium hydrogen phosphate. According to an embodimentof the present invention, the at least one potassium salt according to(i) comprises neither potassium dihydrogen phosphate nor a potassiumsalt of a phosphorus oxyacid wherein the molar ratio of potassiumrelative to phosphorus in the potassium salt of the at least onephosphorus oxyacid is in the range of from 0.6 to 1.4. According to anembodiment of the present invention, the at least one potassium saltaccording to (i) comprises neither potassium dihydrogen phosphate nor apotassium salt of a phosphorus oxyacid wherein the molar ratio ofpotassium relative to phosphorus in the potassium salt of the at leastone phosphorus oxyacid is in the range of from 0.6 to 1.4 nordipotasssium hydrogen phosphate.

According to (i), a liquid feed stream is provided comprising the atleast one potassium salt as dissolved potassium salt. Regarding theconcentration of the at least one potassium salt in the liquid feedstream is concerned, no specific restriction exist. Preferably, theconcentration of the at least one dissolved potassium salt in the liquidfeed stream provided in (i) is at least 10%, preferably in the range offrom 10 to 100%, preferably from 20 to 100%, more preferably from 30 to100%, more preferably from 40 to 100% of the solubility limit of the atleast one potassium salt in the liquid feed stream provided in (i).

The term “solubility limit of the at least one potassium salt in theliquid feed stream” as used in the context of the present inventionrelates to the saturation concentration of the at least one potassiumsalt in the liquid feed stream, where by adding more of the at least onepotassium salt, the concentration of the at least one potassium salt assolute in the liquid feed stream does not increase and at least one ofthe at least one potassium salt would begin to precipitate. Thesolubility limit of the at least one potassium salt in the liquid feedstream will depend on the composition of the liquid feed stream and theconditions such as the temperature at which, and the pressure underwhich, the liquid feed stream is provided in (i). Determining thesolubility limit of the at least one potassium salt in the liquid feedstream is an easy and straight-forward task for the skilled personknowing said conditions and said composition of a given liquid feedstream. A simple procedure to evaluate whether the amount of the atleast one potassium salt being added is above the solubility limit ispassing the liquid feed stream before entering the epoxidation reactorthrough a filter and measure the pressure drop across the filter. If thepressure drop across the filter increases with time on stream and atleast one of the at least one potassium salt is found on the filter whenit is taken offline, the amount of the at least one potassium salt beingadded is already above the solubility limit.

Preferably in (i), the molar ratio of potassium comprised in the atleast one potassium salt relative to hydrogen peroxide comprised in theliquid feed stream is in the range of from 5×10⁻⁶:1 to 1000×10⁻⁶:1,preferably from 25×10⁻⁶:1 to 500×10⁻⁶:1, more preferably from 50×10⁻⁶:1to 250×10⁻⁶:1. The molar amount of the potassium comprised in the atleast one potassium salt relates to the total molar amount of potassiumcomprised in all potassium salts according to (i). Preferred rangesinclude, for example 50×10⁻⁶:1 to 150×10⁻⁶:1 or 100×10⁻⁶:1 to 200×10⁻⁶:1or 150×10⁻⁶1 to 250×10⁶:1.

Further preferably in (i), the molar ratio of potassium relative tohydrogen peroxide in the liquid feed stream is in the range of from5×10⁻⁶:1 to 1000×10⁻⁶:1, preferably from 25×10⁻⁶:1 to 500×10⁻⁶:1, morepreferably from 50×10⁻⁶:1 to 250×10⁻⁶:1. Preferred ranges include, forexample 50×10⁻⁶:1 to 150×10⁻⁶:1 or 100×10⁻⁶:1 to 200×10⁻⁶:1 or150×10⁻⁶:1 to 250×10⁻⁶:1.

Generally, the molar ratio of water relative to acetonitrile in theliquid feed stream provided in (i) is not subject to any specificrestrictions. Preferably, said molar ratio may have any value resultingfrom the respective preferred concentrations of water and acetonitrileas described above. More preferably, in the liquid feed stream providedin (i), passed into the epoxidation reactor and subjected to epoxidationreactor in (ii), the molar ratio of water relative to acetonitrile is atmost 1:4, more preferably in the range of from 1:50 to 1:4, preferablyfrom 1:15 to 1:4.1, more preferably from 1:10 to 1:4.2.

Preferably, the liquid feed stream provided in (i) comprises

-   the acetonitrile in amount of from 60 to 75 weight-%, preferably    from 60 to 65 weight-%, based on the total weight of the liquid feed    stream;-   the hydrogen peroxide in an amount of from 6 to 10 weight-%,    preferably from 7 to 9 weight-%, based on the total weight of the    liquid feed stream;-   the water in a molar ratio of water relative to acetonitrile of at    most 1:4, preferably in the range of from 1:50 to 1:4, preferably    from 1:15 to 1:4.1, more preferably from 1:10 to 1:4.2;-   the propene with a molar ratio of propene relative to hydrogen    peroxide comprised in the liquid feed stream in the range of from    1:1 to 1.5:1, preferably from 1.1:1 to 1.4:1;-   the at least one dissolved potassium in a molar ratio of potassium    comprised in the at least potassium salt relative to hydrogen    peroxide in the liquid feed stream in the range of from 5×10⁻⁶:1 to    1000×10⁻⁶:1, preferably from 25×10^(−6:)1 to 500×10⁻⁶:1, more    preferably from 50×10⁻⁶:1 to 250×10⁻⁶:1; and-   optionally the propane with a molar ratio of propane relative to the    sum of propene and propane in the range of from 0.0001:1 to 0.15:1,    preferably from 0.001:1 to 0.05:1;

Preferably, at least 95 weight-%, preferably from 95 to 100 weight-%,more preferably from 98 to 100 weight-% of the liquid feed streamprovided in (i) consist of propene, hydrogen peroxide, acetonitrile,water, the at least one potassium salt, and optionally propane.

Preferably, the liquid feed stream provided in (i), preferably passed asthe sole feed stream into the epoxidation reactor, is free of ammoniumdihydrogen phosphate. More preferably, the liquid feed stream providedin (i), preferably passed as the sole feed stream into the epoxidationreactor, is free of ammonium phosphate, ammonium hydrogen phosphate andammonium dihydrogen phosphate. More preferably, the liquid feed streamprovided in (i), preferably passed as the sole feed stream into theepoxidation reactor, is free of ammonium carbonate, ammonium hydrogencarbonate, ammonium dihydrogen phosphate, ammonium hydrogen phosphate,ammonium phosphate, ammonium hydrogen pyrophosphate, ammoniumpyrophosphate, ammonium chloride, ammonium nitrate, and ammoniumacetate. More preferably, the liquid feed stream provided in (i),preferably passed as the sole feed stream into the epoxidation reactor,is free of an ammonium salt. The term “free of” as used in this contextof the present invention relates to a concentration of a respectivecompound of at most 2 weight-ppm, preferably at most 1 weight-ppm, basedon the total weight of the liquid feed stream. Therefore, the presentinvention also relates to the process as described above, wherein theliquid feed stream provided in (1), preferably passed as the sole feedstream into the epoxidation reactor, contains ammonium NH₄ ⁺ in amountof at most 2 weight-ppm, preferably at most 1 weight-ppm, based on thetotal weight of the liquid feed stream.

Preferably, the liquid feed stream provided in (i), preferably passed asthe sole feed stream into the epoxidation reactor, contains sodium in amolar ratio of sodium relative to hydrogen peroxide in the range of from1×10⁻⁶:1 to 250×10⁻⁵:1, preferably from 5×10⁻⁶:1 to 50×10³¹ ⁶:1.

Preferably, the liquid feed stream provided in (i), preferably passed asthe sole feed stream into the epoxidation reactor, does not comprisedissolved sodium dihydrogen phosphate (NaH₂PO₄), more preferably neitherdissolved sodium dihydrogen phosphate nor dissolved disodium hydrogenphosphate (Na₂HPO₄), more preferably neither dissolved sodium dihydrogenphosphate nor dissolved disodium hydrogen phosphate nor dissolved sodiumphosphate (Na₃PO₄).

Generally, the liquid feed stream can be provided in (i) according toany conceivable method. Preferably, the liquid feed stream is providedin (i) by combining at least four individual streams wherein a firststream comprises hydrogen peroxide, a second stream comprises propeneand optionally propane, a third stream comprises acetonitrile andoptionally water, and a fourth stream comprises at least one potassiumsalt in an amount so that the potassium salt is dissolved in the liquidfeed stream provided in (i).

These at least four individual stream can be combined in every suitablyorder. Preferably, the stream comprising the at least one potassium saltis combined with the stream comprising hydrogen peroxide, and theresulting combined stream is combined with a stream which results fromcombining the stream comprising acetonitrile and the stream comprisingpropene and optionally propane. The thus obtained stream is the liquidstream provided in (i).

Therefore, the present invention also relates to the process asdescribed above, wherein in (i), the liquid feed stream is provided bycombining a stream comprising hydrogen peroxide, a stream comprisingacetonitrile and optionally water, and a stream comprising propene andoptionally propane, wherein an aqueous stream comprising the at leastone dissolved potassium salt is combined with the stream comprisinghydrogen peroxide, or with the stream comprising acetonitrile andoptionally water, or with the stream comprising propene and optionallypropane, or with a mixed stream of two or three of these streams,preferably with the stream comprising hydrogen peroxide.

Preferably, the stream comprising propene additionally comprises propanewherein preferably at least 98 weight-%, more preferably at least 99weight-%, more preferably at least 99.5 weight-%, more preferably atleast 99.9 weight-% of the stream consist of propene and propane.Preferably, the weight ratio of propene relative to propane in thestream is at least 7:3. For example, commercially available propene canbe employed which may be either a polymer grade propene or a chemicalgrade propene. Typically, polymer grade propene has a propene content inthe range of from 99 to 99.8 weight-% and a propane content in the rangeof from 0.2 to 1 weight-%. Chemical grade propene typically has apropene content in the range of from 92 to 98 weight-% and a propanecontent in the range of from 2 to 8 weight-%. Preferably, a stream isemployed having a propene content in the range of from 99 to 99.8weight-% and a propane content in the range of from 0.2 to 1 weight-%.

Preferably, the stream comprising propene and optionally propene is freeof potassium cations (K⁺) and free of phosphorus (P) in the form ofanions of at least one phosphorus oxyacid. The term “free of potassiumcations (K⁺)” as used in this context of the present invention refers toa stream comprising propene and optionally propane, containing potassiumcations (K⁺) in an amount of less than 1 weight-ppm, preferably lessthan 0.1 weight-ppm, based on the total weight of the stream. The term“free of phosphorus (P) in the form of anions of at least one phosphorusoxyacid” as used in this context of the present invention refers to astream comprising propene and optionally propane, containing phosphorus(P) in the form of anions of at least one phosphorus oxyacid in anamount of less than 1 weight-ppm, preferably less than 0.1 weight-ppm,based on the total weight of the stream.

According to the process of the present invention, it is conceivablethat in addition to the stream comprising propene and optionally propanewhich is used for providing the liquid feed stream in (i), a furtherstream comprising propene and optionally propane may be employed. Thisfurther stream is preferably formed in step (iv) of the presentinvention described hereinbelow, wherein the epoxidation mixture removedaccording to (iii) is subjected to distillation. In step (iv), inaddition to the bottoms stream comprising propylene oxide, acetonitrileand water and being depleted of propene and optionally propane, adistillation top stream is obtained being enriched in propene andoptionally propane. This top stream, optionally after work-up, can berecycled to the epoxidation reaction as part of the liquid feed streamprovided in (i). The volume ratio of the fresh stream comprising propeneand optionally propane relative to the recycled stream comprisingpropene and optionally propane is in the range of from 0.1:1 to 20:1,preferably from 1:1 to 10:1, more preferably from 2:1 to 5:1.

Preferably, in the continuous process of the present invention, thestream comprising acetonitrile which is used for providing the liquidfeed stream in (i) at least partially, preferably essentially consistsof a recycled acetonitrile stream resulting from the work-up of theeffluent stream which is removed in (iii) from the epoxidation reactorand which comprises propylene oxide, acetonitrile, water, at least aportion of the at least one potassium salt, optionally propene, andoptionally propane. During the work-up of the effluent stream, it ispreferred to remove essentially all compounds other than acetonitrileand water from the stream and recycle the thus purified stream back tothe epoxidation reaction. According to a preferred work-up of thepresent invention, the stream comprising propene and optionally propaneas described above is combined with the acetonitrile recycle stream,either after the final purification stage of the acetonitrile recyclestream or before the final purification stage or final purificationstages of the acetonitrile recycle stream. Preferably, the streamcomprising propene and optionally propane as described above is combinedwith the acetonitrile recycle stream before the final purificationstages, more preferably before a work-up stage where a stream comprisingacetonitrile and water is subjected to a phase separation, preferably aliquid-liquid phase separation and where this phase separation iscarried out using the stream comprising propene and optionally propaneas separation-promoting compound. Optionally, after this separationstage, the resulting acetonitrile recycle stream, now additionallycontaining propene and optionally propane, can be subjected to furtherpurification. An especially preferred work-up of the effluent streamremoved according to step (iii) is described in detail hereinbelow.Preferably, the acetonitrile recycle stream to which the streamcomprising propene and optionally comprising propane had been added andwhich had been preferably subjected to phase separation and optionalfurther purification has a 5 composition of which preferably at least 98weight-%, more preferably at least 99 weight-%, more preferably at least99.5 weight-% consist of acetonitrile, water, and propene. Morepreferably, at least 75 weight-%, more preferably in the range of from75 to 90 weight-%, more preferably from 80 to 85 weight-% of the recyclestream consist of acetonitrile and water. In the recycle stream, themolar ratio of acetonitrile relative to water is preferably at most 1:9,more preferably in the range of from 1:50 to 1:9, preferably from 1:25to 1:9, more preferably from 1:25 to 1:10. A preferred process forworking up the effluent stream and recycling the acetonitrile isdescribed hereinbelow.

For starting the continuous process of the present invention and forcompensating any losses of acetonitrile in the course of the work-up ofthe effluent stream obtained in (iii), a part of the stream comprisingacetonitrile used for providing the liquid feed stream in (i) can be amake-up acetonitrile stream. Preferably, the make-up acetonitrile streamis a chemical grade acetonitrile stream having an acetonitrile contentof preferably at least 99.5 weight-%, more preferably at least 99.7weight-%, more preferably at least 99.8 weight-%. Preferably, during thecontinuous process of the present invention, the weight ratio of therecycled acetonitrile stream relative to the make-up acetonitrile streamis in the range of from 1000:1 to 100:1, preferably from 950:1 to 300:1,more preferably from 900:1 to 500:1.

The stream comprising hydrogen peroxide can be prepared according toevery conceivable method. It is conceivable to obtain the streamcomprising hydrogen peroxide by converting sulphuric acid intoperoxodisulphuric acid by anodic oxidation with simultaneous evolutionof hydrogen at the cathode. Hydrolysis of the peroxodisulphuric acidthen leads via peroxomonosulphuric acid to hydrogen peroxide andsulphuric acid which is thus obtained back. The preparation of hydrogenperoxide from the elements is also conceivable. Depending on thespecific preparation method, the stream comprising hydrogen peroxide canbe, for example, an aqueous or an aqueous; methanolic hydrogen peroxidestream, preferably an aqueous hydrogen peroxide stream. In case anaqueous hydrogen peroxide feed is employed, the content of the streamwith respect to hydrogen peroxide is usually in the range of from 3 to85 weight-%, preferably from 25 to 75 weight-%, more preferably from 30to 50 weight-%, such as from 30 to 40 weight-% or from 35 to 45 weight-%of from 40 to 50 weight-%. Preferably, at least 25 weight-%, morepreferably at least 30 weight-%, more preferably at least 35 weight-% ofthe stream comprising hydrogen peroxide consist of water and hydrogenperoxide. Preferred ranges are from 30 to 80 weight-% or from 35 to 75weight-% or from 40 to 70 weight-%.

According to the present, it is preferred to employ a stream comprisinghydrogen peroxide which is obtained as crude hydrogen peroxide solutionby extraction of a mixture which results from a process known asanthraquinone process by means of which virtually the entire worldproduction of hydrogen peroxide is produced (see, e.g., Ullmann'sEncyclopedia of Industrial Chemistry, 5^(th) edition, volume A 13 (1989)pages 443-466) wherein a solution of an anthraquinone is used containingan alkyl group preferably having of from 2 to 10 carbon atoms, morepreferably at least 5 carbon atoms such as 5 carbon atoms or 6 carbonatoms and where the solvent used usually consists of a mixture of twodifferent solvents. This solution of the anthraquinone is usuallyreferred to as the working solution. In this process, the hydrogenperoxide formed in the course of the anthraquinone process is generallyseparated by extraction from the respective working solution after ahydrogenation/re-oxidation cycle. Said extraction can be performedpreferably with essentially pure water, and the crude aqueous hydrogenperoxide solution is obtained. While it is generally possible to furtherpurify the thus obtained crude aqueous hydrogen peroxide solution bydistillation, it is preferred, according to the present invention, touse such crude aqueous hydrogen peroxide solution which has not beensubjected to purification by distillation. Further, it is generallypossible to subject the crude aqueous hydrogen peroxide solution to afurther extraction stage wherein a suitable extracting agent, preferablyan organic solvent is used. More preferably, the organic solvent usedfor this further extraction stage is the same solvent which is used inthe anthraquinone process. Preferably the extraction is performed usingjust one of the solvents in the working solution and most preferablyusing just the most nonpolar solvent of the working solution. In casethe crude aqueous hydrogen peroxide solution is subjected to suchfurther extraction stage, a so-called crude washed hydrogen peroxidesolution is obtained. According to a preferred embodiment of the presentinvention, the crude washed hydrogen peroxide solution is used ashydrogen peroxide feed. The production of a crude solution is described,for example, in European patent application EP 1 122 249 A1. As to theterm “essentially pure water”, reference is made to paragraph 10, page 3of EP 1 122 249 A1 which is incorporated by reference.

In order to provide a sufficient stability of the hydrogen peroxideduring extraction with water, preferably essentially pure water,suitable stabilizing agents are usually added to the water, preferablythe essentially pure water used. In particular, strong inorganic acidsand/or chelating agents are to be mentioned. According to preferredextraction processes, small amounts of nitrates and/or phosphates andpyrophosphates, respectively, are added as stabilizing agents, either asacids or as sodium salts. These stabilizing agents are usually added inamounts so that the crude aqueous hydrogen peroxide solution containsfrom 50 to 400 weight-ppm sodium cations, from 100 to 700 weight-ppmphosphorus calculated as phosphate (PO₄ ³⁻), and from 50 to 400weight-ppm nitrate anions, in each case calculated with respect tohydrogen peroxide contained in the crude aqueous hydrogen peroxidesolution. Preferred ranges are, for example, from 50 to 200 weight-ppmor from 50 to 100 weight-ppm of sodium cations, from 100 to 500weight-ppm or from 100 to 300 weight-ppm of phosphorus, and 50 to 200weight-ppm or 50 to 100 weight-ppm of nitrate. Further, it isconceivable that other stabilizing agents such as stannites like sodiumstannite (Na₂SnO₂) and/or organic phosphonic acids, in particularorganic diphosphonic acids like etidronic acid are used. Preferably, theaqueous hydrogen peroxide stream comprises sodium with a molar ratio ofsodium relative to hydrogen peroxide in the range of from 1×10⁻⁶:1 to250×10⁻⁶:1, more preferably from 5×10⁻⁶:1 to 50×10⁻⁶:1.

Therefore, the present invention relates to the process as definedabove, wherein the stream comprising hydrogen peroxide is an aqueoushydrogen peroxide stream having a hydrogen peroxide concentration in therange of from 25 to 75 weight-%, preferably from 30 to 50 weight-%,based on the total weight of the aqueous hydrogen peroxide stream,wherein the aqueous hydrogen peroxide stream further comprises sodiumwith a molar ratio of sodium relative to hydrogen peroxide in the rangeof from 1×10⁻⁶:1 to 250×10⁻⁶:1, preferably from 5×10⁻⁶:1 to 50×10⁻⁶:1.

Preferably, the liquid feed stream passed into the reactor in (ii) has atemperature in the range of from 0 to 60° C., more preferably from 10 to55° C., more preferably from 25 to 50° C. Preferably, the liquid feedstream passed into the reactor in (ii) is at a pressure in the range offrom 14 to 100 bar, more preferably from 14.5 to 50 bar, more preferablyfrom 15 to 25 bar. Therefore, the present invention relates to theprocess as described above, wherein the liquid feed stream passed intothe reactor in (ii) has a temperature in the range of from 0 to 60° C.,preferably from 25 to 50° C., and is at a pressure in the range of from14 to 100 bar, preferably from 15 to 25 bar.

Step (ii)

The Catalyst Comprising a Titanium Zeolite of Framework Structure TypeMWW

According to step (ii) of the process of the present invention, theliquid feed stream provided in (i) is passed into an epoxidation reactorcomprising a catalyst comprising a titanium zeolite of frameworkstructure type WNW The term “titanium zeolite of framework structuretype MWW” as used in the context of the present invention, also referredto as “TiMWW”, relates to a zeolite of framework structure MWW whichcontains titanium as isomorphous substitution element in the zeoliticframework. Preferably, the zeolitic framework is essentially free ofaluminum and essentially consists of silicon, titanium, and oxygen.Preferably, at least 99 weight-%, more preferably at least 99.5weight-%, more preferably at least 99.9 weight-% of the zeoliticframework consist of silicon, titanium, and oxygen. Optionally, thetitanium zeolite of framework structure type MWW may compriseextra-framework titanium which is to be understood as every titaniumspecies which is not part of the MWW zeolitic framework. The preparationof TiMWW catalysts is described, for example, in U.S. 2007043226 A1, inparticular in Examples 3 and 5 of U.S. 2007043226 A1.

The titanium content of the titanium zeolite of framework structure typeMWW is not subject to any specific restrictions. Preferably, thetitanium zeolite of framework structure type MWW comprised in thecatalyst in (ii) contains titanium, calculated as elemental titanium, inan amount in the range of from 0.1 to 5 weight-%, more preferably from0.2 to 4 weight-%, more preferably from 0.5 to 3 weight-%, morepreferably from 1 to 2 weight-%, based on the total weight of thetitanium zeolite of framework structure type MWW. Therefore, the presentinvention relates to the process as described above, wherein thetitanium zeolite of framework structure type MWW comprised in thecatalyst in (ii) contains titanium, calculated as elemental titanium, inan amount in the range of from 0.1 to 5 weight-%, preferably from 1 to 2weight-%, silicon, based on the total weight of the titanium zeolite offramework structure type MWW.

In addition to the titanium, the titanium zeolite of framework structuretype MWW may comprise at least one further element other than titanium,silicon, and oxygen. Generally, it is conceivable that this at least onefurther element is an isomorphous substitution element which is part ofthe MWW zeolitic framework structure. Preferably, this at least onefurther element is not an isomorphous substitution element. Such afurther element which is not an isomorphous substitution element can beapplied to the zeolite by, for example, a spray process, a wetimpregnation process such as an incipient wetness process, or any othersuitable process. Preferably, the at least one further element isselected from the group consisting of Al, Zr, V, Nb, Ta, Cr, Mo, W, Mn,Fe, Co, Ni, Zn, Ga, Ge, In, Sn, Pb, and a combination of two or more,preferably from the group consisting of Zr, V, Nb, Ta, Cr, Mo, W, Mn,Fe, Co, Ni, Zn, Ga, Ge, In, Sn, Pb, and a combination of two or more.More preferably, the titanium zeolite of framework structure type MWWcontains zinc as further element in addition to titanium, silicon, andoxygen. More preferably, the titanium zeolite of framework structuretype MWW contains zinc as the sole further element in addition totitanium, silicon, and oxygen. More preferably, the titanium zeolite offramework structure type MWW contains zinc as the sole further elementin addition to titanium, silicon, and oxygen wherein at least 99weight-%, more preferably at least 99.5 weight-%, more preferably atleast 99.9 weight-% of the zeolitic framework structure consist ofsilicon, titanium, and oxygen. More preferably, in case the titaniumzeolite of framework structure type MWW contains zinc as the solefurther element, at least 99 weight-%, more preferably at least 99.5weight-%, more preferably at least 99.9 weight-% of the titanium zeoliteof framework structure type MWW consist of zinc, titanium, silicon, andoxygen; this titanium zeolite of framework structure type MWW whichcontains zinc as the sole further element is also referred to as“ZnTiMWW”.

The zinc content of the titanium zeolite of framework structure type MWWis not subject to any specific restrictions. Preferably, the titaniumzeolite of framework structure type MWW comprised in the catalyst in(ii) contains zinc, calculated as elemental zinc, in an amount in therange of from 0.1 to 5 weight-%, more preferably from 0.2 to 4 weight-%,more preferably from 0.5 to 3 weight-%, more preferably from 1 to 2weight-%, based on the total weight of the titanium zeolite of frameworkstructure type MWW. Therefore, the present invention relates to theprocess as described above, wherein the titanium zeolite of frameworkstructure type MWW comprised in the catalyst in (ii) contains zinc,calculated as elemental zinc, in an amount in the range of from 0.1 to 5weight-%, preferably from 1 to 2 weight-%, based on the total weight ofthe titanium zeolite of framework structure type MWW.

The catalyst according to (ii), comprising the titanium zeolite offramework structure type MWW, can consist of the titanium zeolite offramework structure type MWW, preferably consist of the TiMWW or theZnTiMWW as described. In such cases, the catalyst can be the titaniumzeolite of framework structure type MWW in the form of the zeoliticpowder which can be molded, for example as a granules, a microspheresuch as a microsphere obtained from spray drying or by a spraygranulation, a shaped body having, for example, the shape of a pellet, atablet, a cylinder, a wheel, a star, a sphere, and so forth.

Preferably, the catalyst according to (ii), comprising the titaniumzeolite of framework structure type MWW, preferably the TiMWW or theZnTiMWW, is prepared as a molding comprising the titanium zeolite offramework structure type MWW, preferably the TiMWW or the ZnTiMWW, bysuitably mixing the titanium zeolite of framework structure type MWWwith at least one binder and/or with at least one binder precursor, andoptionally at least one pore-forming agent and/or at least oneplasticizing agent. The moldings may be shaped in every conceivablegeometry such as strands, for example having rectangular, triangularhexagonal, quadratic, oval, or circular cross-section, stars, tablets,spheres, hollow cylinders, and the like. Examples of such binders aremetal oxides, such as, for example, SiO₂, Al₂O₃, TiO₂, ZrO₂ or MgO orclays or mixtures of two or more of these oxides or mixed oxides of atleast two of Si, Al, Ti, Zr, and Mg, with SiO₂ being preferred.Pore-forming agent such as mesopore-forming agents include polymericvinyl compounds, such as polyalkylene oxides like polyethylene oxides,polystyrene, polyacrylates, polymethacrylates, polyolefins, polyamidesand polyesters. Pasting agents include organic, in particularhydrophilic polymers, such as carbohydrates like cellulose, cellulosederivatives, such as methyl cellulose, and starch, such as potatostarch, wallpaper plaster, polyacrylates, polymethacrylates, polyvinylalcohol, polyvinyl pyrrolidone, polyisobutene or polytetrahydrofuran.The use of water, alcohols or glycols or mixtures thereof, such asmixtures of water and alcohol, or water and glycol, such as for examplewater and methanol, or water and ethanol, or water and propanol, orwater and propylene glycol, as pasting agents may be mentioned.Preferably, the catalyst according to (ii), is employed as a moldinghaving the shape of an extrudates, preferably an extrudates having alength of preferably from 1 to 10 mm, more preferably of from 1 to 7 mm,more preferably of from 1 to 5 mm, and a diameter preferably of from 0.1to 5 mm, more preferably of from 0.2 to 4 mm, more preferably of from0.5 to 2 mm. In particular as far as the preferred catalyst according to(ii) is concerned comprising the ZnTiMWW, it is preferred to employ thiscatalyst in the form of a micropowder or in the form of a molding,wherein the molding preferably contains said micropowder.

Said catalyst used according to step (ii) of the present invention inthe form of a micropowder, comprising the ZnTiMWW, is preferablycharacterized by the following features and embodiments, including thecombinations of embodiments according to the given dependencies:

-   1. A micropowder, the particles of which having a Dv10 value of at    least 2 micrometer, said micropowder comprising mesopores having an    average pore diameter (4 V/A) in the range of from 2 to 50 nm as    determined by Hg porosimetry according to DIN 66133, and comprising,    based on the weight of the micropowder, at least 95 weight-% of a    microporous aluminum-free zeolitic material of structure type MWW    containing titanium and zinc (ZnTiMWW). The Dv10 value is understood    as being determined according to Reference Example 4.1 of the    present invention.-   2. The micropowder of embodiment 1, having a Dv10 value in the range    of from 2 to 5.5 micrometer, preferably from 3 to 5.5 micrometer.-   3. The micropowder of embodiment 1 or 2, having a Dv50 value in the    range of from 7 to 25 micrometer and optionally a Dv90 value in the    range of from 26 to 85 micrometer. The Dv50 and Dv90 values are    understood as being determined according to Reference Example 4.1 of    the present invention.-   4. The micropowder of any of embodiments 1 to 3, wherein the    mesopores have an average pore diameter (4 V/A) in the range of from    10 to 50 nm, preferably of from 15 to 40 nm, more preferably of from    20 to 30 nm, as determined by Hg porosimetry according to DIN 66133.-   5. The micropowder of any of embodiments 1 to 4, additionally    comprising macropores having an average pore diameter (4 V/A) in the    range of from more than 50 nm, said macropores preferably having an    average pore diameter in the range of from 0.05 to 3 micrometer, as    determined by Hg porosimetry according to DIN 66133.-   6. The micropowder of any of embodiments 1 to 5, wherein the    micropores of the ZnTiMWW have an average pore diameter in the range    of from 1.0 to 1.2 nanometer as determined by nitrogen adsorption    according to DIN 66135.-   7. The micropowder of any of embodiments 1 to 6, comprising, based    on the weight of the micropowder, at least 99 weight-%, preferably    at least 99.7 weight-% of the ZnTiMWW.-   8. The micropowder of any of embodiments 1 to 7, wherein the ZnTiMWW    contains zinc in an amount of from 1.0 to 2.0 weight-%, preferably    of from 1.2 to 1.9 weight-%, calculated as Zn and based on the    weight of the ZnTiMWW.-   9. The micropowder of any of embodiments 1 to 8, wherein the ZnTiMWW    contains titanium in an amount of from 1.0 to 2.0 weight-%,    preferably of from 1.2 to 1.8 weight-%, calculated as Ti and based    on the weight of the ZnTiMWW.-   10. The micropowder of any of embodiments 1 to 9, having a    crystallinity, as determined by X-ray diffraction (XRD) analysis, of    at least (80+/−10) %, preferably of at least (85+/−10) %. The    crystallinity is understood as being determined according to    Reference Example 4.7 of the present invention.-   11. The micropowder of any of embodiments 1 to 10, comprising, based    on the total weight of the micropowder and calculated as element,    less than 0.001 weight-%, preferably less than 0.0001 weight-% of a    noble metal, preferably selected from the group consisting of gold,    silver, platinum, palladium, iridium, ruthenium, osmium, and a    mixture of two or more thereof, more preferably selected from the    group consisting of gold, platinum, gold, and a mixture of two or    more thereof.-   12. The micropowder of any of embodiments 1 to 11, comprising, based    on the total weight of the micropowder and calculated as element,    less than 0.1 weight-%, preferably less than 0.01 weight-% of boron.-   13. The micropowder of any of embodiments 1 to 12, having a bulk    density of in the range of from 80 to 100 g/ml.-   14. The micropowder of any of embodiments 1 to 13, being a spray    powder, preferably obtainable or obtained by spray-drying.

Further, said catalyst used according to step (ii) of the presentinvention in the form of a molding, comprising the ZnTiMWW, ispreferably characterized by the following features and embodiments,including the combinations of embodiments according to the givendependencies:

-   1. A molding, comprising a microporous aluminum-free zeolitic    material of structure type MWW containing titanium and zinc    (ZnTiMWW), said molding preferably comprising a micropowder    comprising, based on the weight of the micropowder, at least 95    weight-% of a microporous aluminum-free zeolitic material of    structure type MWW containing titanium and zinc (ZnTiMWW), said    molding more preferably comprising the micropowder according to any    of the micropowder embodiments 1 to 14 as described hereinabove, the    molding preferably further comprising at least one binder,    preferably a silica binder.-   2. The molding of embodiment 1, comprising mesopores having an    average pore diameter in the range of from 4 to 40 nm, preferably    from 20 to 30 nm as determined by Hg porosimetry according to DIN    66133.-   3. The molding of embodiment 1 or 2, having a crystallinity, as    determined by XRD analysis, of at least (55+/−10) %, preferably in    the range of from ((55 to 75)+/−10) %.

The crystallinity is understood as being determined according toReference Example 4.7 of the present invention.

-   4. The molding of any of embodiments 1 to 3, comprising the    micropowder in an amount in the range of from 70 to 80 weight-% and    the silica binder in an amount of from 30 to 20 weight-%, the    micropowder together with the silica binder constituting at least 99    weight-% of the molding, wherein the molding has a concentration of    silanol groups with respect to the total number of Si atoms of at    most 6%, preferably at most 3%, as determined according to ²⁹Si MAS    NMR. The concentration of the silanol groups is understood as being    determined according to Reference Example 4.2 of the present    invention.-   5. The molding of any of embodiments 1 to 4, being a strand having    circular cross-section and a diameter in the range of from 1.5 to    1.7 mm and having a crush strength of at least 5 N, preferably in    the range of from 5 to 20 N, more preferably in the range of from 12    to 20 N, the crush strength being determined by crush strength test    machine Z2.5/TS1S according to the method as described in Reference    Example 4.3 of the present invention.-   6. The molding of any of embodiments 1 to 5, the ²⁹Si—NMR spectrum    of said molding comprising six peaks at the following position    -   peak 1 at −98+/−x ppm,    -   peak 2 at −104+/−x ppm,    -   peak 3 at −110+/−x ppm,    -   peak 4 at −113+/−x ppm,    -   peak 5 at −115+/−x ppm,    -   peak 6 at −118+/−x ppm,    -   with x in any of the peaks being 1.5, preferably 1.0, more        preferably 0.5,    -   wherein Q which is defined as        Q=100*{[a ₁ +a ₂ ]/[a ₄ +a ₅ +a ₆ ]}/a ₃        is at most 2.5, preferably at most 1.6, preferably at most 1.4,        with [a₁+a₂] being the sum of the peak areas of peaks 1 and 2,        and [a₄ +a₅ +a₆ ] being the sum of the peak areas of peaks 4, 5,        and 6, and a₃ being the peak area of peak 3. These ²⁹Si—NMR        characteristics are understood as being determined according the        Reference Example 4.4 of the present invention.-   7. The molding of any of embodiments 1 to 6, having a water uptake    in the range of from 3 to 8 weight-%, preferably from 4 to 7    weight-%. The water uptake is understood as being determined    according to Reference Example 4.5 of the present invention.-   8. The molding of any of embodiments 1 to 7, the infrared spectrum    of said molding comprising a band in the region of (3700-3750)+/−20    cm⁻¹ and a band in the region of (3670-3690) +/−20 cm⁻¹, wherein the    intensity ratio of the band in the region of (3700-3750) +/−20 cm ⁻¹    relative to the band in the region of (3670-3690) +/−20 cm⁻¹ is at    most 1.5, preferably at most 1.4. These IR characteristics are    understood as being determined according the Reference Example 4.6    of the present invention.

Further, a preferred process for the preparation of said catalystaccording to (ii) in the form of a micropowder and/or molding,comprising the ZnTiMWW, is characterized by the following features andembodiments, including the combinations of embodiments according to thegiven dependencies:

-   1. A process comprising    -   (a) providing a suspension containing a microporous        aluminum-free zeolitic material of structure type MWW containing        titanium and zinc (ZnTiMWW);    -   (b) subjecting the suspension provided in (a) to spray-drying to        obtain a micropowder;    -   (c) optionally calcining the micropowder obtained in (b),    -   wherein the micropowder obtained in (b) or (c), preferably in        (c), is preferably the micropowder according to any of said        micropowder embodiments 1 to 14 as described above.-   2. The process of embodiment 1, wherein the suspension provided    in (a) has a solid content in the range of from 5 to 25 weight-%,    preferably of from 10 to 20 weight-%, the suspension preferably    being an aqueous suspension.-   3. The process of embodiment 1 or 2, wherein the ZnTiMWW according    to (a) contains zinc in an amount of from 1.0 to 2.0 weight-%,    preferably of from 1.2 to 1.9 weight-%, calculated as Zn, and    titanium in an amount of from 1.0 to 2.0 weight-%, preferably of    from 1.2 to 1.8 weight-%, calculated as Ti and based on the weight    of the ZnTiMWW,-   4. The process of any of embodiments 1 to 3, wherein in (b), a    spray-apparatus, preferably a spray-tower is used for spray-drying    the suspension, said apparatus having at least one spray-nozzle,    preferably at least one two-component nozzle, said nozzle having a    diameter in the range of from 3.5 to 4.5 mm.-   5. The process of any of embodiments 1 to 4, wherein in (b), a    spray-apparatus, preferably a spray-tower is used for spray-drying    the suspension, said apparatus being operated with a nozzle gas    having a temperature in the range of from 20 to 50° C., preferably    of from 20 to 30° C., and a drying gas having a temperature in the    range of from 250 to 350° C., preferably of from 275 to 325° C.,    said nozzle gas preferably being an inert gas, more preferably    technical nitrogen, and said drying gas preferably being an inert    gas, more preferably technical nitrogen.-   6. The process of any of embodiments 1 to 5, wherein in (c), the    micropowder is calcined at a temperature in the range of from 600 to    700° C. for a duration in the range of from 0.5 to 6 h.-   7. The process of any of embodiments 1 to 6, further comprising    -   (d) shaping the micropowder obtained in (b) or (c) to obtain a        molding;    -   (e) optionally drying and/or calcining the molding obtained in        (d).-   8. The process of embodiment 7, wherein the shaping according to (d)    comprises    -   (aa) mixing the micropowder with a binder or a binder precursor,        preferably a silica binder or a silica binder precursor, wherein        the weight ratio of the ZnTiMWW contained in the micropowder        relative to silica contained in or resulting from the silica        binder is in the range of from 3:7 to 1:4, to obtain a mixture;    -   (bb) shaping the mixture obtained in (aa) to obtain the molding,        said shaping preferably comprising subjecting the mixture        obtained in (aa) to extrusion from which preferably strands are        obtained having a diameter preferably in the range of from 1.0        to 2.0 mm, more preferably of from 1.5 to 1.7 mm.-   9. The process of embodiment 8, wherein in (aa), a carbohydrate    and/or water is/are added as pasting agent.-   10. The process of embodiment 8 or 9, wherein the mixing in (aa) is    carried out for a duration in the range of from 15 to 60 min,    preferably of from 30 to 55 min, more preferably of from 40 to 50    min.-   11. The process of any of embodiments 7 to 10, wherein in (d), no    mesopore-forming agent selected from the group consisting of    polyalkylene oxides such as polyethylene oxides, polystyrene,    polyacrylates, polymethacrylates, polyolefins, polyamides, and    polyesters is added.-   12. The process of any of embodiments 7 to 11, wherein in (e), the    molding is dried at a temperature in the range of from 100 to    150° C. for a duration in the range of from 10 to 20 h and calcined    at a temperature in the range of from 500 to 600° C. for a duration    in the range of from 0.5 to 2 h.-   13. The process of any of embodiments 7 to 12, further comprising    -   (f) subjecting the molding obtained in (d) or (e), preferably in        (e), to a water-treatment;    -   (g) optionally drying and/or calcining the water-treated        molding,    -   wherein the molding obtained in (f) or (g), preferably in (g),        is preferably the molding according to any of said molding        embodiments 1 to 8 as described above.-   14. The process of embodiment 13, wherein in (f), the    water-treatment comprises treating the molding with liquid water in    an autoclave under autogenous pressure at a temperature in the range    of from 100 to 200° C., preferably of from 125 bis 175° C., more    preferably of from 140 to 150° C. for a period of from 2 to 24    hours, preferably of from 6 to 10 h.-   15. The process of embodiment 13 or 14, wherein in (f), the weight    ratio of the molding relative to the water is in the range of from    0.02 to 0.08, preferably of from 0.03 to 0.07, more preferably of    from 0.04 to 0.06.-   16. The process of any of embodiments 13 to 15, wherein in (g), the    water-treated molding is dried at a temperature in the range of from    100 to 150° C. for a duration in the range of from 10 to 20 h and    calcined at a temperature in the range of from 400 to 500° C. for a    duration in the range of from 1 to 3 h.-   17. The process of any of embodiments 7 to 16, wherein the molding    is not subjected to steaming.

Regarding said preferred process for the preparation of said catalystaccording to (b) in the form of a micropowder and/or a molding,comprising the ZnTiMWW, described above by embodiments 1 to 17, theZnTiMWW based on which the suspension in embodiment 1. (a) is provided,can be prepared according to all conceivable methods. For example, it ispossible to prepare a microporous aluminum-free zeolitic material ofstructure type MWW containing titanium (TiMWW) and subject the TiMWW toa suitable treatment to obtain the ZnTiMWW. Further, it is possible toprepare an aluminum-free zeolitic material of structure type MAN (MWW)and subject the MWW to a suitable treatment to obtain the ZnTiMWWwherein, for example, both Zn and Ti are suitably incorporated in theMWW. Further, it is conceivable to prepare aluminum-free zeoliticmaterial of structure type MWW wherein, during the synthesis of theMWW-type framework, Ti is introduced and the resulting material issubjected to a suitable treatment to incorporate Zn, or Zn is introducedand the resulting material is subjected to a suitable treatment toincorporate Ti, or both Zn and Ti are introduced. As conceivable methodsfor the preparation of TiMWW, the processes as described, for example,in U.S. Pat. No. 6,114,551, or in Wu et al., “Hydrothermal Synthesis ofa novel Titanosilicate with MWW Topology”, Chemistry Letters (2000), pp.774-775 may be mentioned. Preferably, an aluminum-free zeolitic materialof structure type MWW containing Ti (TiMWW) is prepared in a firststage, and in a second stage, the TiMWW is subjected to a suitabletreatment to obtain the ZnTiMWW. More preferably, the ZnTiMWW isprepared according to a process comprising

-   (I) preparing an aluminum-free zeolitic material of structure type    MWW containing boron (B-MWW);-   (II) deboronating the B-MWW to obtain an aluminum-free zeolitic    material of structure type MWW (MWW);-   (III) incorporating titanium (Ti) into the MWW to obtain an    aluminum-free zeolitic material of structure type MWW containing Ti    (TiMWW);-   (IV) preferably acid-treating the TiMWW;-   (V) subjecting the TiMWW to zinc (Zn) impregnation to obtain the    ZnTiMWW,

Preferably, in stage (I), the B-MWW is prepared by a process whosepreferred steps and conditions are defined by the following embodiments1 to 28 and the respective dependencies as indicated:

-   1. A process for preparing an aluminum-free boron containing    zeolitic material comprising the framework structure MWW (B-MWW),    comprising    -   (a) hydrothermally synthesizing a B-MWW precursor from a        synthesis mixture containing water, a silicon source, a boron        source, and an MWW template compound obtaining the B-MWW        precursor in its mother liquor, the mother liquor having a pH        above 9;    -   (b) adjusting the pH of the mother liquor, obtained in (a) and        containing the B-MWW precursor, to a value in the range of from        6 to 9;    -   (c) separating the B-MWW precursor from the pH-adjusted mother        liquor obtained in (b) by filtration in a filtration device.-   2. The process of embodiment 1, wherein in (a), at least 95    weight-%, preferably at least 99 weight-%, more preferably at least    99.9 weight-% of the synthesis mixture consist of the water, the    silicon source, the boron source, and the template compound.-   3. The process of embodiment 1 or 2, wherein in (a), the silicon    source is selected from the group consisting of fumed silica,    colloidal silica, and a mixture thereof, the silicon source    preferably being colloidal silica, more preferably    ammonia-stabilized silica, the boron source is selected from the    group consisting of boric acid, borates, boron oxide; and a mixture    of two or more thereof, the boron source preferably being boric    acid, and the MWW template compound selected from the group    consisting of piperidine, hexamethylene imine,    N,N,N,N′,N′,N′-hexamethyl-1,5-pentanediammonium ion,    1,4-bis(N-methylpyrrolidinium) butane, octyltrimethylammonium    hydroxide, heptyltrimethyl-ammonium hydroxide,    hexyltrimethylammonium hydroxide, N,    N,N-trimethyl-1-adamantyl-ammonium hydroxide, and a mixture of two    or more thereof, the MWW template compound preferably being    piperidine.-   4. The process of any of embodiments 1 to 3, wherein in (a), the    synthesis mixture contains the boron source, calculated as elemental    boron, relative to the silicon source, calculated as elemental    silicon, in a molar ratio in the range of from 0.4:1 to 2.0:1,    preferably from 0.6:1 to 1.9:1, more preferably from 0.9:1 to 1.4:1,    the water relative to the silicon source, calculated as elemental    silicon, in a molar ratio in the range of from 1:1 to 30:1,    preferably from 3:1 to 25:1, more preferably from 6:1 to 20:1; and    the template compound relative to the silicon source, calculated as    elemental silicon, in a molar ratio in the range of from 0.4:1 to    2.0:1, preferably from 0.6:1 to 1.9:1, more preferably from 0.9:1 to    1.4:1.-   5. The process of any of embodiments 1 to 4, wherein in (a), the    hydrothermal synthesizing is carried out at a temperature in the    range of from 160 to less than 180° C., preferably from 170 to 175°    C., for a period of time in the range of from 1 to 72 h, preferably    from 6 to 60 h, more preferably from 12 to 50 h.-   6. The process of any of embodiments 1 to 5, wherein in (a), the    hydrothermal synthesizing is carried out at least partially under    stirring.-   7. The process of any of embodiments 1 to 6, wherein in (a), the    synthesis mixture additionally contains a seeding material,    preferably a zeolitic material comprising the framework structure    MWW, more preferably a boron containing zeolitic material comprising    the framework structure MWW.-   8. The process of embodiment 7, wherein the synthesis mixture    contains the seeding material, relative to the silicon source, in a    weight ratio in the range of from 0.01:1 to 1:1, preferably from    0.02:1 to 0.5:1, more preferably from 0.03:1 to 0.1:1, calculated as    amount of seeding material in kg relative to silicon contained in    the silicon source calculated as silicon dioxide in kg.-   9. The process of any of embodiments 1 to 8, wherein the pH of the    mother liquor obtained from (a) is above 10, preferably in the range    of from 10.5 to 12, more preferably from 11 to 11.5.-   10. The process of any of embodiments 1 to 9, wherein in (b), the pH    of the mother liquor obtained in (a) is adjusted to a value in the    range of from 6.5 to 8.5, preferably from 7 to 8.-   11. The process of any of embodiments 1 to 10, wherein in (b), the    pH is adjusted by a method comprising    -   (aa) adding an acid to the mother liquor obtained from (a)        containing the B-MWW precursor, wherein the adding is preferably        carried out at least partially under stirring.-   12. The process of embodiment 11, wherein in (aa), the adding is    carried out at a temperature in the range of from 20 to 70° C.,    preferably from 30 to 65° C., more preferably from 40 to 60° C.-   13. The process of embodiment 11 or 12, wherein in (aa), the acid is    an inorganic acid, preferably an aqueous solution containing the    inorganic acid.-   14. The process of embodiment 13, wherein the inorganic acid is    selected from the group consisting of phosphoric acid, sulphuric    acid, hydrochloric acid, nitric acid, and a mixture of two or more    thereof, the inorganic acid preferably being nitric acid.-   15. The process of any of embodiments 11 to 14, the method    additionally comprising    -   (bb) stirring the mother liquor to which the acid was added        according to (aa), wherein during (bb), no acid is added to the        mother liquor.-   16. The process of embodiment 15, wherein in (bb), the stirring is    carried out at a temperature in the range of from 20 to 70° C.,    preferably from 25 to 65° C., more preferably from 30 to 60° C.-   17. The process of any of embodiments 1 to 16, wherein in (b), the    size of the particles contained in the mother liquor, expressed by    the respective Dv10, Dv50, and Dv90 value, is increased for at least    2%, preferably at least 3%, more preferably at least 4.5% regarding    Dv10, for at least 2%, preferably at least 3%, more preferably at    least 4.5% regarding Dv50, and for at least 5%, preferably at least    6%, more preferably at least 7% regarding Dv90.-   18. The process of any of embodiments 1 to 17, wherein the    pH-adjusted mother liquor obtained from (b) has a solids content in    the range of from 1 to 10 weight-%, preferably from 4 to 9 weight-%,    more preferably from 7 to 8 weight-%, based on the total weight of    the pH-adjusted mother liquor obtained from (b).-   19. The process of any of embodiments 1 to 18, wherein the    pH-adjusted mother liquor obtained from (b) has a filtration    resistance in the range of from 10 to 50 mPa*s/m², preferably from    15 to 45 mPa*s/m², more preferably from 20 to 40 mPa*s/m².-   20. The process of any of embodiments 1 to 19, further comprising    -   (d) washing the B-MWW precursor obtained from (c), preferably        the filter cake obtained from (c), wherein the washing is        preferably performed using water was washing agent.-   21. The process of embodiment 20, wherein in (d), the filter cake    obtained from (c) is has a washing resistance in the range of from    10 to 50 mPa*s/m², preferably from 15 to 45 mPa*s/m², more    preferably from 20 to 40 mPa*s/m².-   22. The process of embodiment 20 or 21, wherein the washing is    carried out until the conductivity of the filtrate is at most 300    microSiemens/cm, preferably at most 250 microSiemens/cm, more    preferably at most 200 microSiemens/cm.-   23. The process of any of embodiments 1 to 22, further comprising    -   (e) drying the B-MWW precursor obtained from (c), preferably        from (d), at a temperature in the range of from 20 to 50° C.,        preferably from 20 to 40° C., more preferably from 20 to 30° C.,        wherein the drying is preferably carried out by subjecting the        BAUM to a gas stream, preferably a nitrogen stream.-   24. The process of any of embodiments 1 to 23, wherein the residual    moisture of the B-MWW precursor obtained from (c), preferably from    (d), more preferably from (e), is in the range of from 80 to 90    weight-%, preferably from 80 to 85 weight-%.-   25. The process of any of embodiments 1 to 24, further comprising    -   (f) preparing a suspension, preferably an aqueous suspension,        containing the B-MWW precursor obtained from to (c), preferably        from (d), more preferably from (e), and having a solids content        in the range of from 10 to 20 weight-%, preferably from 12 to 18        weight-%, more preferably from 14 to 16 weight-%;    -   (g) spray drying the suspension obtained from (f) containing the        B-MWW precursor, obtaining a spray powder;    -   (h) calcining the spray powder obtained from (g) containing the        B-MWW precursor, preferably at a temperature in the range of        from 500 to 700° C., more preferably from 550 to 650° C., more        preferably from 575 to 625° C. for a period of time in the range        of from 1 to 24 h, preferably from 2 to 18 h, more preferably        from 6 to 12 h, obtaining a spray powder of which at least 99        weight-%, more preferably at least 99.5 weight-% consist of the        B-MWW.-   26. The process of embodiment 25, wherein in (h), the calcining is    carried out in continuous mode, preferably in a rotary calciner,    preferably at a throughput in the range of from 0.5 to 20 kg spray    powder per h.-   27. The process of embodiment 25 or 26, wherein the degree of    crystallinity of the B-MWW contained in the spray powder obtained    from (h) is at least (75±5) %, preferably at least (80±5) %, as    determined via XRD.-   28. The process of any of embodiments 25 to 27, wherein the BET    specific surface area of the B-MWW contained in the spray powder    obtained from (h) is at least 300 m²/g, preferably in the range of    from 300 to 500 m²/g, as determined according to DIN 66131.

Preferably, stage (II) is carried by a process whose preferred steps andconditions are defined by the following embodiments 1 to 7 and therespective dependencies as indicated:

-   1. A process for the preparation of a zeolitic material, comprising    -   (a) providing the boron-containing zeolitic material of        structure ype MWW (B-MWW) obtained according to stage (I);    -   (b) deboronating the B-MWW by treating the B-MWW with a liquid        solvent system thereby obtaining a deboronated B-MWW (MWW);    -   wherein the liquid solvent system is selected from the group        consisting of water, monohydric alcohols, polyhydric alcohols,        and mixtures of two or more thereof, and wherein said liquid        solvent system does not contain an inorganic or organic acid or        a salt thereof, the acid being selected from the group        consisting of hydrochloric acid, sulfuric acid, nitric acid,        phosphoric acid, formic acid, acetic acid, propionic acid,        oxalic acid, and tartaric acid.-   2. The process of embodiment 1, wherein the liquid solvent system    does not contain an inorganic or organic acid, or a salt thereof.-   3. The process of embodiment 1 or 2, wherein the liquid solvent    system is selected from the group consisting of water, methanol,    ethanol, propanol, ethane-1,2-diol, propane-1,2-diol,    propane-1,3-diol, propane-1,2,3-triol, and mixtures of two or more    thereof, preferably water.-   4. The process of any of embodiments 1 to 3, wherein the treating    according to (b) is carried out at a temperature in the range of    from 50 to 125° C.-   5. The process of any of embodiments 1 to 4, wherein the treating    according to (b) is carried out for a time in the range of from 6 to    20 h.-   6. The process of any of embodiments 1 to 5, wherein the treating    according to (b) is carried out in at least 2 separate steps,    wherein between at least 2 treating steps, the MWW is dried,    preferably at a temperature in the range of from 100 to 150° C.-   7. The process of any of embodiments 1 to 6, further comprising    -   (c) post-treating the MWW obtained from (b) by a process        comprising        -   (c.1) separating the MWW from the liquid solvent system;        -   (c.2) preferably drying the separated MWW, preferably by            spray-drying;        -   (c.3) optionally calcining the MWW obtained from (c.1) or            (c.2), preferably at temperatures in the range of from 500            to 700° C.

As far as stage (III) is concerned, preferably a suitable startingmixture, preferably an aqueous mixture, containing the WAN and a Ticontaining precursor, and preferably containing at least one suitablemicropore-forming agent, is subjected to hydrothermal crystallizationunder autogenous pressure. It may be conceivable to use at least onesuitable seeding material. As suitable Ti containing precursor,tetraalkylorthotitanates such as tetrabutyl orthotitanate may bementioned by way of example. As suitable micropore-forming agent,piperidine, hexamethylene imine, or mixtures of piperidine andhexamethylene imine may be mentioned by way of example. Preferably, thecrystallization time is in the range of from 4 to 8 days, morepreferably from 4 to 6 days, During hydrothermal synthesis, thecrystallization mixture may be stirred. The temperatures applied duringcrystallization are preferably in the range of from 160 to 200° C., morepreferably from 160 to 180° C. After hydrothermal synthesis, theobtained crystalline zeolitic material TiMWW is preferably suitablyseparated from the mother liquor. All methods of separating the TiMWWfrom its mother liquor are conceivable. These methods include, forexample, filtration, ultrafiltration, diafiltration and centrifugationmethods or, for instance, spray drying processes and spray granulationprocesses. A combination of two or more of these methods can be applied.According to the present invention, the TiMWW is preferably separatedfrom its mother liquid by filtration to obtain a filter cake which ispreferably subjected to washing, preferably with water. Subsequently,the filter cake, optionally further processed to obtained a suitablesuspension, is subjected to spray drying or to ultrafiltration. Prior toseparating the TiMWW from its mother liquor, it is possible to increasethe TiMWW content of the mother liquor by concentrating the suspension.If washing is applied, it is preferred to continue the washing processuntil the washing water has a conductivity of less than 1,000microSiemens/cm, more preferably of less than 900 microSiemens/cm, morepreferably of less than 800 microSiemens/cm, more preferably of lessthan 700 microSiemens/cm. After separation of the TiMWW from its motherliquor, preferably achieved via filtration, and after washing, thewashed filter cake containing the TiMWW is preferably subjected topre-drying, for example by subjecting the filter cake to a suitable gasstream, preferably a nitrogen stream, for a time preferably in the rangeof from 4 to 10 h, more preferably from 5 to 8 h. Subsequently, thepre-dried filter cake is preferably dried at temperatures in the rangeof from 100 to 300° C., more preferably from 150 to 275° C., morepreferably from 200 to 250° C. in a suitable atmosphere such astechnical nitrogen, air, or lean air, preferably in air or lean air,Such drying can be accomplished, for example, by spray-drying. Afterdrying, the TiMWW may be subjected to calcination at temperatures in therange of from 500 to 700° C., more preferably from 550 to 675° C., morepreferably from 600 to 675° C. in a suitable atmosphere such astechnical nitrogen, air, or lean air, preferably in air or lean air.Preferably, no calcination is carried out according to (III).

Preferably, stages (III) and (IV) are carried out by a process whosepreferred steps and conditions are defined by the following embodiments1 to 27 and the respective dependencies as indicated:

-   1. A process for the preparation of a titanium-containing zeolitic    material having an MWW framework structure comprising    -   (a) providing the deboronated crystalline zeolitic material MWW        obtained according to stage (II);    -   (b) incorporating titanium into the zeolitic material provided        in (a) comprising        -   (b.1) preparing an aqueous synthesis mixture containing the            zeolitic material provided in (i), an MWW template compound            and a titanium source, wherein the molar ratio of the WNW            template compound relative to Si, calculated as SiO₂ and            contained in the zeolitic material provided in (a), is in            the range of from 0.5:1 to 1.4:1;        -   (b.2) hydrothermally synthesizing a titanium-containing            zeolitic material having an WNW framework structure from the            aqueous synthesis mixture prepared in (b.1), obtaining a            mother liquor comprising the titanium-containing zeolitic            material having an WWI framework structure;    -   (c) spray-drying the mother liquor obtained from (b.2)        comprising the titanium-containing zeolitic material having an        MWW framework structure.-   2. The process of embodiment 1, wherein in (b.1), the MWW template    compound is selected from the group consisting of piperidine,    hexamethylene imine, N,N,N,N′,N′,N′-hexamethyl-1,5-pentanediammonium    ion, 1,4-bis(N-methylpyrrolidini-um)butane, octyltrimethylammo-nium    hydroxide, heptyltrimethylammonium hydroxide, hexyltrimethylammonium    hydroxide, and a mixture of two or more thereof, the WNW template    compound preferably being piperidine.-   3. The process of embodiment 1 or 2, wherein in (b.1), the titanium    source is selected from the group consisting of tetrabutyl    orthotitanate, tetraisopropyl orthotitanate, tetra-ethyl    orthotitanate, titanium dioxide, titanium tetrachloride, titanium    tert-butoxide, and a mixture of two or more thereof, the titanium    source preferably being tetrabutyl orthotitanate.-   4. The process of any of embodiments 1 to 3, wherein in the aqueous    synthesis mixture in (b.1), the molar ratio of Ti, calculated as    TiO₂ and contained in the titanium source, relative to Si,    calculated as SiO₂ and contained in the zeolitic material having a    molar ratio B₂O₃:SiO₂ of at most 0.02:1, is in the range of from    0.005:1 to 0.1:1, preferably from 0.01:1 to 0.08:1, more preferably    from 0.02:1 to 0.06:1.-   5. The process of any of embodiments 1 to 4, wherein in the aqueous    synthesis mixture in (b.1), the molar ratio of H₂O relative to Si,    calculated as SiO₂ and contained in the zeolitic material having a    molar ratio B₂O₃:SiO₂ of at most 0.02:1, is in the range of from 8:1    to 20:1, preferably from 10:1 to 18:1, more preferably from 12:1 to    16:1.-   6. The process of any of embodiments 1 to 5, wherein in the aqueous    synthesis mixture in (b.1), the molar ratio of the MWW template    compound relative to Si, calculated as SiO₂ and contained in the    zeolitic material provided in (i), is in the range of from 0.5:1 to    1.7:1, preferably from 0.8:1 to 1.5:1, more preferably from 1.0:1 to    1.3:1.-   7. The process of any of embodiments 1 to 6, wherein in (b.2), the    hydrothermal synthesizing is carried out at a temperature in the    range of from 80 to 250° C., preferably from 120 to 200° C., more    preferably from 160 to 180° C.-   8. The process of any of embodiments 1 to 7, wherein in (b.2), the    hydrothermal synthesizing is carried out for a period in the range    of from 10 to 100 h, more preferably from 20 to 80 h, more    preferably from 40 to 60 h.-   9. The process of any of embodiments 1 to 8, wherein in (b.2), the    hydrothermal synthesizing is carried out in a closed system under    autogenous pressure.-   10. The process of any of embodiments 1 to 9, wherein neither during    (b.2), nor after (b.2) and before (c), the titanium-containing    zeolitic material having an MWW framework structure is separated    from its mother liquor.-   11. The process of any of embodiments 1 to 10, wherein the mother    liquor subjected to (c) comprising the titanium-containing zeolitic    material having an MWW framework structure has a solids content,    optionally after concentration or dilution, in the range of from 5    to 25 weight-%, more preferably from 10 to 20 weight-%, based on the    total weight of the mother liquor comprising the titanium-containing    zeolitic material.-   12. The process of any of embodiments 1 to 11, wherein during    spray-drying in (c), the drying gas inlet temperature is in the    range of from 200 to 350° C. and the drying gas outlet temperature    is in the range of from 70 to 190° C.-   13. The process of any of embodiments 1 to 12, wherein the zeolitic    material having an MWW framework structure obtained from (c) has a    Si content in the range of from 30 to 40 weight-%, calculated as    elemental Si, a total organic carbon content (TOC) in the range of    from 0 to 14 weight-%, and a Ti content of from 2.1 to 2.8 weight-%,    calculated as elemental titanium, in each case based on the total    weight of the zeolitic material.-   14. The process of any of embodiments 1 to 13, further    comprising (d) treating the titanium-containing zeolitic material    having an MWW framework structure obtained from (iii) with an    aqueous solution having a pH of at most 5.-   15. The process of embodiment 14, wherein after (c) and before (d),    the spray-dried titanium-containing zeolitic material having an MWW    framework structure obtained from (c) is not subjected to    calcination.-   16. The process of embodiment 14 or 15, wherein in (d), the weight    ratio of the aqueous solution relative to the titanium-containing    zeolitic material having an MWW framework structure is in the range    of from 10:1 to 30:1, preferably from 15:1 to 25:1, more preferably    from 18:1 to 22:1.-   17. The process of any of embodiments 14 to 16, wherein in (d), the    aqueous solution comprises an inorganic acid, preferably selected    from the group consisting of phosphoric acid, sulphuric acid,    hydrochloric acid, nitric acid, and a mixture of two or more    thereof, the aqueous solution preferably comprising nitric acid.-   18. The process of any of embodiments 14 to 17, wherein in (d), the    aqueous solution has a pH in the range of from 0 to 5, preferably    from 0 to 3, more preferably from 0 to 2.-   19. The process of any of embodiments 14 to 18, wherein in (d), the    titanium-containing zeolitic material having an MWW framework    structure is treated with the aqueous solution at a temperature in    the range of from 50 to 175° C., preferably from 70 to 125° C., more    preferably from 95 to 105° C.-   20. The process of any of embodiments 14 to 19, wherein in (d), the    titanium-containing zeolitic material having an WNW framework    structure is treated with the aqueous solution for a period in the    range of from 0.1 to 6 h, preferably from 0.3 to 2 h, more    preferably from 0.5 to 1.5 h.-   21. The process of any of embodiments 14 to 20, wherein the treating    according to (d) is carried out in a closed system under autogenous    pressure.-   22. The process of any of embodiments 14 to 21, further comprising    -   (e) separating the titanium-containing zeolitic material having        an MWW framework structure obtained from (d) from the aqueous        solution, optionally followed by washing the separated        titanium-containing zeolitic material having an WNW framework.-   23. The process of embodiment 22, wherein (e) comprises drying the    separated and optionally washed titanium-containing zeolitic    material having an MWW framework structure.-   24. The process of any of embodiments 14 to 23, further comprising    -   (f) preparing a suspension, preferably an aqueous suspension        containing the titanium-containing zeolitic material having an        MWW framework structure obtained from (d), preferably from (e),        said suspension having a solids content preferably in the range        of from 5 to 25 weight-%, more preferably from 10 to 20        weight-%, based on the total weight of the suspension, and        subjecting the suspension to spray-drying.-   25. The process of embodiment 24, wherein during spray-drying, the    drying gas inlet temperature is in the range of from 200 to 330° C.    and the drying gas outlet temperature is in the range of from 120 to    180° C.-   26. The process of any of embodiments 14 to 25, further comprising    -   (g) calcining the titanium containing zeolitic material having        an MWW framework structure obtained from (d), preferably from        (e), more preferably from (f), wherein the calcining is        preferably carried out at a temperature in the range of from 400        to 800° C., more preferably from 600 to 700° C.-   27. The process of embodiment 26, wherein in (vii), the calcining is    carried out in continuous mode, preferably with a rate in the range    of from 0.2 to 2.0 kg zeolitic material per hour, more preferably    from 0.5 to 1.5 kg zeolitic material per hour.

According to stage (V), the TiMWW preferably obtained according to stage(IV) is subjected to a suitable Zn treatment to obtain the ZnTiMWW usedfor the preparation of the suspension according to (a). Generally, asfar as (V) is concerned, no specific restrictions exist provided thatabove-defined preferred ZnTiMWW can be obtained having the preferred Znand Ti content. Most preferably, stage (V) comprises at least onesuitable impregnation stage, more preferably at least one wetimpregnation stage. Concerning this impregnation stage, it is preferredto contact the TiMWW preferably as obtained according to (IV) iscontacted with at least one suitable Zn-containing precursor in at leastone suitable solvent (wet impregnation), most preferably water. Assuitable Zn-containing precursor, water-soluble Zn salts are especiallypreferred, with zinc acetate dihydrate being especially preferred. It isfurther preferred to prepare a solution of the Zn-containing precursor,preferably an aqueous solution, and to suspend the TiMWW in thissolution. Further preferably, impregnation is carried out at elevatedtemperatures, relative to room temperature, preferably in the range offrom 75 to 125° C., more preferably from 85 to 115° C., for a timepreferably in the range of from 3.5 to 5 h, more preferably from 3 to 6h. Stirring the suspension during impregnation is preferred. After theimpregnation, the obtained ZnTiMWW is preferably suitably separated fromthe suspension. All methods of separating the ZnTiMWW from thesuspension are conceivable. Especially preferably, separation is carriedout via filtration, ultrafiltration, diafiltration or centrifugationmethods. A combination of two or more of these methods can be applied.According to the present invention, the ZnTiMWW is preferably separatedfrom the suspension by filtration to obtain a filter cake which ispreferably subjected to washing, preferably with water. If washing isapplied, it may be preferred to continue the washing process until thewashing water has a conductivity of less than 1,000 microSiemens/cm,more preferably of less than 900 microSiemens/cm, more preferably ofless than 800 microSiemens/cm, more preferably of less than 700microSiemensicm. Subsequently, the preferably washed filter cake issubjected to pre-drying, for example by subjecting the filter cake to asuitable gas stream, preferably a nitrogen stream, for a time preferablyin the range of from 5 to 15 h, more preferably from 8 to 12.

An especially preferred process for the preparation of a preferredcatalyst according to step (ii) of the process of the present inventionin the form of a molding, comprising the ZnTiMWW, and the respectivecharacterization of this catalyst is described in Reference Example 2 ofthe present invention. A preferred process for the preparation of apreferred catalyst according to step (ii) of the process of the presentinvention in the form of a molding, comprising the TiMWW, and therespective characterization of this catalyst is described in ReferenceExample 3 of the present invention.

Therefore, the present invention preferably relates to a continuousprocess for the preparation of propylene oxide, comprising

-   (i) providing a liquid feed stream comprising propene, hydrogen    peroxide, acetonitrile, water, optionally propane, and at least one    dissolved potassium salt;-   (ii) passing the feed stream provided in (i) into an epoxidation    reactor comprising a catalyst comprising a titanium zeolite of    structure type MWW comprising zinc, and subjecting the feed stream    to epoxidation reaction conditions in the epoxidation reactor,    obtaining a reaction mixture comprising propylene oxide,    acetonitrile, water, the at least one potassium salt, optionally    propene, and optionally propane:-   (iii) removing an effluent stream from the epoxidation reactor, the    effluent stream comprising propylene oxide, acetonitrile, water, at    least a portion of the at least one potassium salt, optionally    propene, and optionally propane.

Therefore, the present invention especially preferably relates to acontinuous process for the preparation of propylene oxide, comprising

-   (i) providing a liquid feed stream comprising propene, hydrogen    peroxide, acetonitrile, water, optionally propane, and dissolved    potassium formate, potassium acetate, or a mixture thereof,    preferably potassium formate;-   (ii) passing the feed stream provided in (i) into an epoxidation    reactor comprising a catalyst comprising a titanium zeolite of    structure type MWW comprising zinc, and subjecting the feed stream    to epoxidation reaction conditions in the epoxidation reactor,    obtaining a reaction mixture comprising propylene oxide,    acetonitrile, water, the potassium formate, potassium acetate, or a    mixture thereof, preferably the potassium formate, optionally    propene, and optionally propane;-   (iii) removing an effluent stream from the epoxidation reactor, the    effluent stream comprising propylene oxide, acetonitrile, water, at    least a portion of the potassium formate, potassium acetate, or a    mixture thereof, the preferably potassium formate, optionally    propene, and optionally propane.    Epoxidation Reaction

According to step (ii) of the process of the present invention, theliquid feed stream provided in (i) is passed into an epoxidation reactorcomprising a catalyst comprising the titanium zeolite of frameworkstructure type MWW, and the liquid feed stream is subjected toepoxidation reaction conditions in the epoxidation reactor. During theepoxidation reaction, a reaction mixture is formed which comprisespropylene oxide, acetonitrile, water, the at least one potassium salt,optionally propene, and optionally propane.

Generally, the continuous epoxidation reaction in (ii) can be carriedout in any appropriate way. Preferably, the reaction in (ii) is carriedout in at least one continuously operated reactor such as a tube reactoror a tube bundle reactor which preferably contains at least one coolingjacket surrounding the at least one tube. If the reaction in (ii) iscarried out in such a reactor containing at least one cooling jacket,the term “reaction temperature” as used herein refers to the temperatureof the cooling medium when entering the cooling jacket.

Generally, the continuous epoxidation reaction in (ii) can be carriedout in any appropriate way. Preferably, the reaction in (ii) is carriedout in at least one continuously operated reactor such as a tube reactoror a tube bundle reactor which preferably contains at least one coolingjacket surrounding the at least one tube. If the reaction in (ii) iscarried out in such a reactor containing at least one cooling jacket,the term “reaction temperature” as used herein refers to the temperatureof the cooling medium when entering the cooling jacket.

The catalyst comprising the titanium zeolite of framework structure typeWNW can be employed in every conceivable form described hereinabove,including a powder, a micropowder, preferably a spray-powder, as amolding comprising a powder, or as a molding comprising micropowder,preferably a spray-powder. Preferably, the catalyst comprising thetitanium zeolite of framework structure type MWW is employed as amolding comprising a powder or a micropowder, preferably a spray-powder,more preferably as a molding comprising a micropowder, preferably aspray-powder. Regarding a preferred micropowder, reference is made tothe micropowder characterized by the respective micropowder embodiments1 to 14 hereinabove. Regarding a preferred molding, reference is made tothe molding characterized by the respective molding embodiments 1 to 8hereinabove.

The catalyst used in step (ii) of the present invention can be arrangedin the reactor in every conceivable manner. Preferably, the catalyst isarranged as fluidized bed or as fixed bed, more preferably as fixed bed.Therefore, the present invention also relates to the process asdescribed above, wherein in (ii), the catalyst comprising a titaniumzeolite of framework structure type MWW is present in the reactor asfixed-bed catalyst.

As mentioned above, the liquid feed stream provided in (i) is passedinto the reactor in (i) and passed the catalyst preferably present asfixed bed. During the epoxidation reaction, the catalyst loading ispreferably in in the range of from 0.05 to 1.25 h⁻¹, preferably from 0.1to 1 h⁻¹, more preferably from 0.2 to 0.7 h⁻¹, wherein the catalystloading is defined as the ratio of the mass flow rate in kg/h ofhydrogen peroxide contained in liquid feed stream provided in (i)divided by the amount in kg of catalyst comprising a titanium zeolite ofstructure type WNW comprised in the epoxidation reactor in (ii). Theterm “the epoxidation conditions comprise” as used in this context ofthe present invention relates to an epoxidation reaction in step (ii)wherein in at least 90%, preferably at least 95% of the catalyst bed inthe reactor and during at least 90%, preferably at least 95% of theoverall reaction time, the catalyst loading is in the above-definedranges.

During the epoxidation reaction in (ii), the temperature of the reactionmixture in the reactor is preferably controlled, more preferably kept inpreferred ranges. In order to control the temperature of the reactionmixture, internal and/or external temperature control means can be used.The term “intern temperature control means” as used in this context ofthe present invention relate to means which are arranged in the reactor.The term “external temperature control means” as used in this context ofthe present invention relate to means which are arranged outside thereactor. Preferably, the temperature of the reaction mixture iscontrolled by external temperature control means, more preferably via aheat transfer medium which is preferably passed through a suitablejacket, which jacket preferably surrounds the reactor. In case atube-bundle reactor is used as reactor, the jacket preferably surroundsall tubes of the tube-bundle. Therefore, the present invention relatesto the process as described above, wherein during subjecting the liquidfeed stream provided in (i) to epoxidation reaction conditions in (ii),the temperature of the reaction mixture is controlled using a heattransfer medium, preferably by passing the heat transfer medium througha jacket of the epoxidation reactor.

Preferably, during the epoxidation reaction in (ii), the reactiontemperature is in the range of from 20 to 100° C., more preferably from25 to 90° C., more preferably from 30 to 80° C., more preferably from 35to 70° C., more preferably from 40 to 60° C. The term “reactiontemperature” as used in this context of the present invention relates tothe temperature of the heat transfer medium prior to controlling of thetemperature of the reaction mixture, preferably to the temperature ofthe heat transfer medium at the entrance of the jacket of theepoxidation reactor, through which jacket the heat transfer medium ispassed. Therefore, the present invention relates to the process asdescribed above, wherein in (ii), the epoxidation conditions comprise,preferably consist of an epoxidation reaction temperature in the rangeof from 20 to 100° C., preferably from 30 to 80° C., more preferablyfrom 40 to 60 ° C., wherein the epoxidation reaction temperature isdefined as the temperature of the heat transfer medium prior tocontrolling of the temperature of the reaction mixture, preferably asthe temperature of the heat transfer medium at the entrance of thejacket of the epoxidation reactor. The term “the epoxidation conditionscomprise” as used in this context of the present invention relate to anepoxidation reaction in step (ii) wherein for at least 98%, preferablyat least 99%, more preferably at least 99.9% of the overall reactiontime, the reaction temperature is in the above-defined ranges. The term“overall reaction time” as used in this context of the present inventionrelates to the reaction time a given catalyst bed is used before it iseither discarded or subjected to regeneration. In particular at thebeginning of an epoxidation reaction in (ii) when the catalyst is fresh,i.e, at the start-up of the epoxidation reaction in (ii), the reactiontemperature can be outside the above-mentioned ranges for a short periodof time. Preferably, the flow rate of the heat transfer medium is chosenso that the temperature difference between its inlet temperature and itsoutlet temperature is at most 3 K, more preferably at most 2 K, morepreferably at most 1 K.

Preferably, during the epoxidation reaction in (ii), the epoxidationreaction pressure is in the range of from 14 to 100 bar, more preferablyfrom 14.5 to 50 bar, more preferably from 15 to 32 bar, more preferablyfrom 15 to 25 bar. The term “epoxidation reaction pressure” as used inthis context of the present invention relates to the pressure at theexit of the epoxidation reactor where the effluent is removed from thereactor according to (iii). Therefore, the present invention relates tothe process as described above, wherein in (ii), the epoxidationconditions comprise, preferably consist of an epoxidation reactionpressure in the range of from 14 to 100 bar, preferably from 15 to 32bar, more preferably from 15 to 25 bar. The term “the epoxidationconditions comprise” as used in this context of the present inventionrelate to an epoxidation reaction in step (ii) wherein for at least 98%,preferably at least 99%, more preferably at least 99.9% of the overallreaction time, the reaction temperature is in the above-defined ranges.The term “overall reaction time” as used in this context of the presentinvention relates to the reaction time a given catalyst bed is usedbefore it is either discarded or subjected to regeneration.

Preferably, the epoxidation reaction according to step (ii) of thepresent invention is carried out at an essentially constant hydrogenperoxide conversion. Preferably, in order to determine the hydrogenperoxide conversion, the molar flow rate of hydrogen peroxide in theeffluent stream removed in (iii), referred to herein as m_(out), iscompared with the molar flow rate of hydrogen peroxide in the liquidfeed stream provided in (i), referred to herein as and wherein thehydrogen peroxide conversion is defined as 100×(1−m_(out)/m_(in)).Preferably, the inlet temperature of the heat transfer medium describedabove is adjusted in the above-mentioned preferred ranges in order tokeep the hydrogen peroxide conversion essentially constant in the rangeof from 80 to 100%, more preferably from 90 to 100%, more preferablyfrom 95 to 100%, more preferably from 99 to 100%, more preferably from99.5 to 100%, more preferably from 99.9 to 100%.

Therefore, the present invention relates to the process as describedabove, wherein in (ii), the epoxidation conditions comprise a hydrogenperoxide conversion in the range of from 80 to 100%, preferably from 90to 100%, more preferably from 99 to 100%, more preferably from 99.5 to100%, more preferably from 99.9 to 100%, wherein the hydrogen peroxideconversion is calculated based on the amount of hydrogen peroxidecomprised in the effluent stream removed in (iii) and the amount ofhydrogen peroxide comprised in the liquid feed stream provided in (i).The term “the epoxidation conditions comprise” as used in this contextof the present invention relate to an epoxidation reaction in step (ii)wherein for at least 98%, preferably at least 99%, more preferably atleast 99.9% of the overall reaction time, the hydrogen peroxideconversion is in the above-defined ranges. The term “overall reactiontime” as used in this context of the present invention relates to thereaction time a given catalyst bed is used before it is either discardedor subjected to regeneration. In particular at the beginning of anepoxidation reaction in (ii) when the catalyst is fresh, i.e. at thestart-up of the epoxidation reaction in (ii), the hydrogen peroxideconversion can be outside the above-mentioned ranges for a short periodof time. Preferably, the reaction temperature is not kept constantduring the reaction but is adjusted continuously or step-wise to allowfor a constant hydrogen peroxide conversion. Generally, due to a certaincatalyst deactivation, the reaction temperature is continuously orstep-wise increased. Preferably, the reaction temperature iscontinuously or step-wise increased by 1 K/d (Kelvin/day) at most, morepreferably by less than 1 K/d.

Preferably, the reaction mixture which is present in the reactor in (ii)is liquid under the epoxidation conditions. Preferably, the reactionmixture consists of one single liquid phase, of two liquid phases, or ofthree or more liquid phases. Preferably, the reaction mixture in thereactor in (ii) consists of one single liquid phase or of two liquidphases, more preferably of one single liquid phase.

Generally, the reactor used in step (ii) of the present invention can bearranged horizontally or vertically. Preferably, the reactor is arrangedvertically. In the preferably vertically arranged reactor, the liquidfeed stream provided in (i) can be passed in up-flow mode or ondown-flow mode, the up-flow mode being preferred. Preferably, comparedwith the direction of the flow of the liquid feed stream, the heattransfer medium is passed through the jacket in co-current mode.

Generally, the epoxidation reaction in (ii) can be carried out in one ormore reactors wherein these reactors can be arranged in parallel or inseries. Preferably, the reaction in (ii) is carried out in one reactoror in at least two reactors, preferably two reactors, which are arrangedin series wherein between two reactors arranged in series, a suitableintermediate treatment can be carried out. If the reaction is carriedout in two reactors arranged in series, it is preferred that the firstreactor is operated as described above, i.e. as isothermal reactor, andthe second reactor, i.e. the downstream reactor, is operated asadiabatic or essentially adiabatic reactor. The term “reactor” as usedherein also encompasses two or more reactors arranged in parallelwherein a feed stream passed is divided in two or more sub-streams, eachsubstream is passed into a reactor, and the effluent streams removedfrom the reactors are combined to obtain the overall effluent stream.Therefore, the epoxidation reaction can be carried out in at least onefirst reactor such as two or more first reactors, for example 2, 3, 4first reactors, which are arranged in parallel and which are preferablyisothermal reactors, and in at least one second reactor such as two ormore second reactors, for example 2, 3, 4 second reactors, which arearranged in parallel and which are preferably adiabatic or essentiallyadiabatic reactors.

If the epoxidation reaction according to (ii) is carried out in tworeactors arranged in series, it is preferred that in the first reactorwhich is preferably an isothermal reactor, the hydrogen peroxideconversion is kept essentially constant in a range of from 80 to 99%,preferably from 85 to 98%, more preferably from 90 to 97% and in thesecond reactor which is preferably designed as adiabatic or essentiallyadiabatic reactor, the overall hydrogen peroxide conversion, i.e. thehydrogen peroxide conversion taking into account the conversion in thefirst and the second reactor, is brought to a value of more than 99preferably at least 99.5%, more preferably at least 99.9%.

In case the reaction according to (ii) is carried out in two reactorsarranged in series without intermediate treatment, it is preferred thatthe reaction comprises

-   (i) providing a liquid feed stream comprising propene, hydrogen    peroxide, acetonitrile, water, the at least one dissolved potassium    salt, and optionally propane;-   (ii-1) passing the liquid feed stream provided in (i) into an    epoxidation reactor comprising a catalyst comprising a titanium    zeolite of framework structure type MWW, and subjecting the liquid    feed stream to epoxidation reaction conditions in the epoxidation    reactor, obtaining a stream leaving the epoxidation reactor, said    stream comprising propylene oxide, acetonitrile, water, the at least    one potassium salt, optionally propane, optionally propene, and    unreacted hydrogen peroxide, wherein the epoxidation reactor is    preferably operated as isothermal reactor;-   (ii-2) passing the stream leaving the epoxidation reaction according    to (ii-1), preferably after admixing with propene optionally admixed    with propane, into an epoxidation reactor comprising a catalyst    comprising a titanium zeolite of framework structure type MWW, and    subjecting the liquid feed stream to epoxidation reaction conditions    in the epoxidation reactor, obtaining a stream leaving the    epoxidation reactor, said stream comprising propylene oxide,    acetonitrile, water, the at least one potassium salt, optionally    propene, and optionally propane; wherein the epoxidation reactor is    preferably operated as adiabatic or essentially adiabatic reactor;-   (iii) removing the stream obtained in (ii-2) as effluent stream, the    effluent stream comprising propylene oxide, acetonitrile, water, at    least a portion of the at least one potassium salt, optionally    propene, and optionally propane;    wherein the molar ratio of potassium comprised in the at least one    potassium salt relative to hydrogen peroxide comprised in the liquid    feed stream provided in (i) is in the range of from 5×10⁻⁶:1 to    1000×10⁻⁶:1, preferably from 25×10^(−6:)1 to 500×10⁻⁶:1, more    preferably from 50×10⁻⁶:1 to 250×10⁻⁶:1.

For this case where the reaction according to (ii) is carried out in tworeactors arranged in series without intermediate treatment, the tworeactors arranged in series can be designed as one reactor comprisingtwo reaction zones, wherein the first reaction zone according to (ii-1)is preferably designed as an isothermal reaction zone and the second,downstream reaction zone according to (ii-2) is preferably designed asan adiabatic or essentially adiabatic reaction zone.

In case the reaction according to (ii) is carried out in two reactorsarranged in series with intermediate treatment, it is preferred that thereaction comprises

-   (i) providing a liquid feed stream comprising propene, hydrogen    peroxide, acetonitrile, water, the at least one dissolved potassium    salt, and optionally propane;-   (ii-1) passing the liquid feed stream provided in (i) into an    epoxidation reactor comprising a catalyst comprising a titanium    zeolite of framework structure type MWW, and subjecting the liquid    feed stream to epoxidation reaction conditions in the epoxidation    reactor, obtaining a stream leaving the epoxidation reactor, said    stream comprising propylene oxide, acetonitrile, water, the at least    one potassium salt, optionally propane, optionally propene, and    unreacted hydrogen peroxide, wherein the epoxidation reactor is    preferably operated as isothermal reactor;-   (ii-2) separating propylene oxide from the stream obtained from    (ii-1), obtaining a stream being enriched in propylene oxide and    depleted of hydrogen peroxide, and a stream being depleted of    propylene oxide and comprising unreacted hydrogen peroxide,    acetonitrile, and water;-   (ii-3) passing the stream being depleted of propylene oxide and    comprising unreacted hydrogen peroxide, acetonitrile, and water,    preferably after admixing with propene optionally admixed with    propane, into an epoxidation reactor comprising a catalyst    comprising a titanium zeolite of framework structure type MWW, and    subjecting the liquid feed stream to epoxidation reaction conditions    in the epoxidation reactor, obtaining a stream leaving the    epoxidation reactor, said stream comprising propylene oxide,    acetonitrile, water, at least a portion of the at least one    potassium salt, optionally propene, and optionally propane; wherein    the epoxidation reactor is preferably operated as adiabatic or    essentially adiabatic reactor;-   (ii-4) preferably combining the stream being enriched in propylene    oxide and depleted of hydrogen peroxide obtained in (ii-2) and the    stream obtained in (ii-3);-   (iii) removing the stream obtained in (ii-3), preferably the    combined stream obtained in (ii-4), as effluent stream, the effluent    stream comprising propylene oxide, acetonitrile, water, at least a    portion of the at least one potassium salt, optionally propene, and    optionally propane;    wherein the molar ratio of potassium comprised in the at least one    potassium salt relative to hydrogen peroxide comprised in the liquid    feed stream provided in (i) is in the range of from 5×10⁻⁶:1 to    1000×10⁻⁶:1, preferably from 25×10⁻⁶:1 to 500×10⁻⁶:1, more    preferably from 50×10⁻⁶:1 to 250×10⁻⁶:1.

According to this process where in the intermediate treatment in (ii-2),propylene oxide is separated from the stream obtained from (ii-1), theseparation is preferably carried out via distillation. Preferably, thestream leaving the epoxidation reactor according to (ii-1), said streamcomprising propylene oxide, acetonitrile, water, at least a portion ofthe at least one potassium salt wherein the molar ratio of potassiumcomprised in the at least one potassium salt relative to hydrogenperoxide comprised in the liquid feed stream provided in (i) is in therange of from 5×10⁻⁶:1 to 1000×10⁻⁶:1, preferably from 25×10⁻⁶:1 to500×10⁻⁶:1, more preferably from 50×10⁻⁶:1 to 250×10⁻⁶:1, optionallypropane, optionally propene, and unreacted hydrogen peroxide, issubjected to a suitable pressure release stage and passed to thepreferred distillation according to (ii-2). Optionally, the possiblyformed gaseous and liquid phases are suitably separated and passed todifferent trays of the distillation tower employed according to (ii-2).Alternatively, the effluent stream can be subjected to said pressurerelease directly in the distillation column employed according to(ii-2). Preferably, the distillation according to (ii-2) is carried outso that at most 10% of the propylene oxide comprised in the streamobtained from (ii-1) are comprised in the top stream, and at least 95%,preferably at least 98% of the hydrogen peroxide comprised in the streamobtained from (ii-1) are comprised in the bottoms stream. The bottomsstream is then preferably passed according to (ii-3) to the downstreamepoxidation reactor where, preferably after admixing propene, theoverall hydrogen peroxide conversion is brought to a value of more than99%, preferably at least 99.5%, more preferably at least 99.9%. In orderto achieve the desired hydrogen peroxide conversion, it is possible tosuitably adjust the temperature of the stream to be fed to thedownstream epoxidation reactor which is preferably an adiabatic oressentially adiabatic reactor.

Step (iii)

Preferably, the effluent stream removed in (iii) comprises

-   the propylene oxide in amount of from 5 to 20 weight-%, preferably    from 8 to 18 weight-%, more preferably 10 to 14 weight-% based on    the total weight of the effluent stream;-   the acetonitrile in amount of from 60 to 75 weight-%, preferably    from 60 to 65 weight-%, based on the total weight of the effluent    stream;-   the water in amount of from 10 to 25 weight-%, preferably from 15 to    20 weight-%, based on the total weight of the effluent stream;-   optionally the propene with a molar ratio of propene relative to    hydrogen peroxide comprised in the feed stream in the range of from    0.005:1 to 0.7:1, preferably from 0.25:1 to 0.45:1;-   the at least one dissolved potassium salt with a molar ratio of    potassium comprised in the at least one potassium salt relative to    hydrogen peroxide comprised in the feed stream in the range of from    5×10⁻⁶:1 to 1000×10⁻⁶:1, preferably from 25×10⁻⁶:1 to 500×10⁻⁶:1,    more preferably from 50×10⁻⁶:1 to 250×10⁻⁶:1;-   optionally the propane, preferably in an amount in the range of from    95 to 100%, preferably from 98 to 100% more preferably from 99 to    100% of the amount contained in the liquid feed stream provided in    (i).

Preferably, at least 95 weight-%, more preferably from 95 to 100weight-%, more preferably from 98 to 100 weight-% of the effluent streamremoved in (iii) consist of propylene oxide, acetonitrile, water, the atleast one potassium salt, optionally propene, and optionally propane.

In addition to the major components described above, the effluent streamremoved in (iii) may contain at least one further by-product orside-product of the epoxidation reaction or at least compound which isformed in additional work-up stages and which is recycled into theepoxidation reaction in the course of the continuous reaction, Such aby-product or side-product may include, for example, oxygen, or at leastone propylene glycol. Therefore, the present invention relates to theprocess as described above, wherein the effluent stream removed in (iii)comprises contains molecular oxygen, preferably with a molar ratio ofthe molecular oxygen comprised in the effluent stream removed in (iii)relative to the hydrogen peroxide comprised in the liquid feed streamprovided in (i) in the range of from 0.05:100 to 2.5:100, preferablyfrom 0.1:100 to 2.25:100, more preferably from 0.15:100 to 42:100.

According to the present invention, the effluent stream removedaccording to (iii) may contain at least one component B wherein thenormal boiling point of the at least one component B is higher than thenormal boiling point of acetonitrile and wherein the decadic logarithmof the octanol-water partition coefficient (log K_(OW)) of the at leastone component B is greater than zero. Regarding the determination of theoctanol-water partition coefficient, reference is made to ReferenceExample 5 hereinbelow. Typically, the at least one component B containedin the effluent stream removed according to (iii) either is a by-productand/or a side-product obtained during the epoxidation reaction in (ii),and/or is a compound which is formed during at least one of the work-upstages being preferably carried out downstream of step (ii) and whichaccumulates if certain process streams of the preferred integratedprocess are recycled into (i), and/or is contained as an impurity in atleast one of the starting materials employed in (i) such as an impurityin the acetonitrile or an impurity in the hydrogen peroxide. Preferably,the at least one component B is propionitrile, 1-nitropropane,2-nitropropane, 3-methylbutanenitrile, n-pentanenitrile, 1-pentanol,2-pentanol, 2-butanone, 2-pentanone, 2-hexanone, 4-methyl-2-heptanone,2,6-dimethyl-4-heptanal, 4,6-dimethyl-2-heptanol,2,6-dimethyl-4-heptanone, 4,6-dimethyl-2-heptanone,2,6-dimethyl-4,6-heptandiol, 2,4-dimethyloxazoline,2,5-dimethyloxazo-line, cis-2,4-dimethyl-1,3-dioxolane,trans-2,4-dimethyl-1,3-dioxolane, at least one impurity contained in thehydrogen peroxide stream employed in (i), or a combination of two ormore of these compounds. Preferably, the at least one impurity containedin the hydrogen peroxide stream employed in (i) is an alkyl phosphatesuch as tris-(2-ethylhexyl) phosphate, a nonyl alcohol such asdiisobutylcarbinol, an alkylcyclohexanol ester such as2-methyl-cyclohexylacetate, an N,N-dialkyl carbonamide such asN,N-dibutylpropionamide, an N-alkyl-N-aryl carbonamide such asN-ethyl-N-phenylbenzamide, an N,N-dialkyl carbamate such as2-ethylhexyl-N-butylcarbamate, a tetraalkyl urea such astetra-n-butylurea, a cyclic urea derivative such as1,3-dihexyltetrahydro-2(1H)-pyrimidone, a phenylalkyl urea such asN,N-dibutyl-N′-methyl-N′-phenylurea, an N-alkyl-2-pyrrolidone such asoctyl pyrrolidone, an N-alkyl caprolactam such as n-octyl caprolactam,or a combination of two or more of these compounds.

Therefore, the present invention relates to the process as describedabove, wherein the effluent stream removed in (iii) comprises

-   the propylene oxide in amount of from 5 to 20 weight-%, preferably    from 8 to 18 weight-%, more preferably 10 to 14 weight-% based on    the total weight of the effluent stream;-   the acetonitrile in amount of from 60 to 75 weight-%, preferably    from 60 to 65 weight-%, based on the total weight of the effluent    stream;-   the water in amount of from 10 to 25 weight-%, preferably from 15 to    20 weight-%, based on the total weight of the effluent stream;-   optionally the propene with a molar ratio of propene relative to    hydrogen peroxide comprised in the feed stream in the range of from    0.005:1 to 0.7:1, preferably from 0.25:1 to 0.45:1;-   the at least one dissolved potassium salt with a molar ratio of    potassium comprised in the at least one potassium salt relative to    hydrogen peroxide comprised in the feed stream in the range of from    5×10⁻⁶:1 to 1000×10⁻⁶:1, preferably from 25×10⁻⁶:1 to 500×10⁻⁶:1,    more preferably from 50×10⁻⁶:1 to 250×10⁻⁶:1;-   optionally the propane, preferably in an amount in the range of from    95 to 100%, preferably from 98 to 100%, more preferably from 99 to    100% of the amount contained in the liquid feed stream provided in    (i);-   the at least one component B in an amount of from 0.01 to 3    weight-%, preferably from 0.015 to 2 weight-%, more preferably from    0.02 to 1 weight-% based on the total weight of the effluent stream.

Preferably, at least 95 weight-%, preferably from 95 to 100 weight-%,more preferably from 98 to 100 weight-% of the effluent stream removedin (iii) consist of propylene oxide, acetonitrile, water, the at leastone potasssium salt, the at least one component B, optionally propene,and optionally propane.

Further Downstream Stages

From the effluent stream removed according to (iii), propylene oxide canbe separated according to any conceivable method. Preferably, theeffluent stream removed in (iii) comprises propene and optionallypropane, and the process of the present invention, in addition to steps(i), (ii), and (iii), further comprises

-   (iv) separating propene, optionally together with propane, and    oxygen which is optionally additionally contained in the effluent    stream, from the effluent stream, obtaining a stream S01 enriched in    propylene oxide, acetonitrile, and water, wherein preferably at    least 99 weight-% of S01 consist of acetonitrile, water, and    propylene oxide; wherein for separation, preferably a fractionation    unit is used, wherein preferably, at the top of the fractionation    unit, liquid acetonitrile, optionally admixed with liquid water, is    added as entraining agent, and wherein S01 is preferably obtained as    bottoms streams;-   (v) separating propylene oxide from S01, obtaining a top stream    comprising propylene oxide and being depleted of acetonitrile and    water.

Preferably, prior to (iv), the effluent stream is subjected to asuitable pressure release stage and passed to the separation stageaccording to (iv). Optionally, the possibly formed gaseous and liquidphases are suitably separated and passed to different trays of thedistillation tower employed according to (iv) if the separationaccording to (iv) is carried via distillation. Alternatively, theeffluent stream can be subjected to said pressure release directly inthe distillation column employed according to (iv); in this case, nopressure release apparatus downstream of the epoxidation stage andupstream of the separation stage according to (iv) would be necessary.Optionally, the temperature of the effluent stream can be suitablyadjusted prior to (iv), preferably after the pressure release stage.

Preferably, in (v), a further stream S02 is obtained, preferably asbottoms stream, which is enriched in acetonitrile and water. Preferably,at least 95 weight-% of S02 consist of acetonitrile and water, whereinmore preferably, the weight ratio of acetonitrile relative to water inthe stream S02 is greater than 1:1. Therefore, the present inventionrelates to the process as described above, which comprises

-   (v) separating propylene oxide from S01, obtaining a top stream    comprising propylene oxide and being depleted of acetonitrile and    water, and obtaining a stream S02, preferably as bottoms stream,    enriched in acetonitrile and water, wherein at least 95 weight-% of    S02 consist of acetonitrile and water, and wherein the weight ratio    of acetonitrile relative to water is greater than 1:1.

Further, the present invention relates to a process comprising

-   (iv) separating propene, optionally together with propane, and    oxygen which is optionally additionally contained in the effluent    stream, from the effluent stream, obtaining a stream S01 enriched in    propylene oxide, acetonitrile, water, and optionally the at least    one component B, wherein preferably at least 99 weight-% of S01    consist of acetonitrile, water, preferably the at least one    component B, and propylene oxide; wherein for separation, preferably    a fractionation unit is used, wherein preferably, at the top of the    fractionation unit, liquid acetonitrile, optionally admixed with    liquid water, is added as entraining agent, and wherein S01 is    preferably obtained as bottoms streams;-   (v) separating propylene oxide from S01, obtaining a top stream    comprising propylene oxide and being depleted of acetonitrile and    water, and obtaining a stream S02, preferably as bottoms stream,    enriched in acetonitrile, water and optionally the at least one    component B, wherein preferably at least 95 weight-% of S02 consist    of acetonitrile, water and preferably the at least one component B,    and wherein the weight ratio of acetonitrile relative to water is    greater than 1:1.

Regarding step (iv), no specific restrictions exist. Preferably, theseparation is carried out so that at least 90 weight-%, more preferablyat least 95 weight-%, more preferably at least 98 weight-%, morepreferably at least 99 weight-% of S01 consist of acetonitrile, water,preferably the at least one component B, and propylene oxide.Preferably, a fractionation unit is employed for the separation in (iv).Further preferably, the separation in (iv) is carried out in at leastone distillation tower, more preferably in one distillation tower. Fromthis distillation tower, S01 is preferably obtained as bottoms stream.Preferably, this distillation tower has from 10 to 30, more preferablyfrom 15 to 25 theoretical trays. The distillation tower is preferablyoperated at a top pressure of from 0.5 to 1.2 bar, more preferably offrom 0.7 to 1.1 bar. In order to facilitate said separation task, it wasfound that it is advantageous to add either liquid acetonitrile or aliquid mixture of acetonitrile with water to the top of the column. Itis believed that this external reflux serves as entraining agent which,among others, prevents propylene oxide from being separated via the topof the distillation tower. According to a preferred embodiment of thepresent invention, a portion of the bottom stream of the distillationtower preferably employed in stage (v) is used. It is also conceivablethat the stream TL2 described hereinbelow or a portion thereof is usedas entraining agent. The amount of TL2 will not be sufficient, andanother stream is to be added. Preferably, the weight ratio of theamount of acetonitrile fed as external reflux to the top of thedistillation tower relative to the weight of the effluent stream removedin (iii) fed into the distillation tower and to be separated in thedistillation tower is in the range of from 1:1 to 4:1 preferably from1.5:1 to 3:1. The temperature of the external reflux is generally in therange of from 2 to 20° C., preferably in the range of from 5 to 15° C.According to the present invention, preferably at least 85 volume %,more preferably at least 90 volume %, more preferably at least 93 volume% of the top stream of the distillation column according to (iv) consistof propene, oxygen, and optionally propane. Depending on its oxygencontent, this top stream can be passed to a further suitable work-upstage wherein the oxygen content is suitably decreased in order toallow, e.g., for recycling the oxygen-depleted stream to be recycled toone or more stages of the present invention, such as a starting materialfor step (ii) of the inventive process like stage (ii-1) or stage(ii-3), or as portion of the stream P described hereinbelow. If theoxygen content of said top stream is reduced, it is preferred to reducethe oxygen by reaction with hydrogen in the presence of a suitablecatalyst. For example, it is possible to use catalysts comprising copperin elemental and/or oxidic form on a support, wherein copper is presenton the support in an amount of 30 to 80 weight-% based on the wholecatalyst and calculated as CuO. Such catalysts can be prepared, forexample, according to the example of EP 0 427 062 A2, catalyst 2, page4, lines 41 to 50 (corresponding to U.S. Pat. No. 5,194,675). In orderto reduce the oxygen content, also other suitable methods areconceivable. Optionally, said top stream, prior to be subjected tohydrogenation, can be compressed and partially condensed wherein aliquid stream is obtained which essentially consists of propene andoptionally propane and acetonitrile and which contains minor amounts ofwater. The non-condensed portion essentially consists of propene andoptionally propane and oxygen and contains a minor amount of waterwherein, compared to the basic stream, the oxygen content is increasedwhile still being in a range so that the mixture is not ignitable. Thisoxygen-enriched stream is then subjected to hydrogenation.

Regarding step (v), no specific restrictions exist. Preferably, theseparation is carried out so that preferably at least 90 weight-%, morepreferably at least 95 weight-%, more preferably at least 99 weight-% ofS02 consist of acetonitrile, water and optionally the at least onecomponent B. More preferably, the weight ratio of acetonitrile relativeto water in S02 is greater than 1:1, preferably in the range of from 2:1to 10:1, more preferably from 2.5:1 to 5:1. Preferably, a fractionationunit is employed for the separation in (v). Further preferably, theseparation in (v) is carried out in at least one distillation tower,more preferably in one distillation tower. Preferably, this tower has offrom 50 to 80, more preferably of from 60 to 70 theoretical trays. Thedistillation tower is preferably operated at a top pressure of from 0.2to 2 bar, more preferably of from 0.4 to 1 bar. Optionally, at least onesuitable polar solvent or a mixture of two or more polar solvents,preferably water, can be added in the upper part of the column asextracting agent.

According to an embodiment of the process of the present invention, theseparation according to step (v) can be carried out by

-   -   introducing S01 into an extractive distillation column;    -   additionally introducing a polar extracting solvent or a mixture        of two or more thereof,    -   preferably water, into said extractive distillation column;    -   distilling propylene oxide overhead from said extractive        distillation column as top stream, wherein the top stream        comprises only minor amounts of acetonitrile such as 500 ppm or        less;    -   compressing said top stream obtained overhead in the previous        step by means of at least one compressor to give a compressed        vapor;    -   condensing the compressed vapor obtained in the previous step        and returning at least part of the heat of condensation to at        least one reboiler employed in the extractive distillation        column.

From this distillation tower according to (v), a top stream is obtainedwhich contains preferably at least 90 weight-%, more preferably at least95 weight-%, more preferably at least 99 weight-% of propylene oxide.Further from this distillation tower, S02 is preferably obtained asbottoms stream which preferably contains 500 weight-ppm at most,preferably 100 weight-ppm at most, and more preferably 60 weight-ppm atmost of propylene oxide, based on the weight of S02, Depending on therequirements on the propylene oxide quality, it is conceivable to usethis propylene oxide fraction without any further purification. It is,however, also conceivable to further purify said propylene oxidefraction, for example in at least one further distillation stage.

From the distillation tower according to (v) or optionally from thefurther distillation stage, a propylene oxide stream is obtained whereinpreferably at least 99.990 weight-%, more preferably at least 99.995weight-%, more preferably at least 99.999 weight-% of said streamconsist of propylene oxide.

Therefore, the present invention also relates to a compositioncomprising at least 99.990 weight-%, preferably at least 99.995weight-%, more preferably at least 99.999 weight-% of propylene oxide,preferably obtainable or obtained by a process comprising steps (iv) and(v) as descrivbed above.

Generally, the stream S02 as described above can be used as acetonitrilerecycle stream which can be used for providing the liquid feed stream in(i). Further, it is possible that the stream SO2 is subjected to furtherwork-up steps before it is used as acetonitrile recycle stream which isused for providing the liquid feed stream in (i). Preferably, the streamS02 is subjected to the further work-up steps described hereinbelow inthe embodiments 1 to 13.

Prior to step (vi) as described below, it is conceivable

-   (v-01) to subject the stream S02 obtained from step (v) to    hydrogenation; and/or-   (v-02) to subject the stream obtained from (v) or from (v-01) to    distillation to obtain a bottoms stream,    wherein the hydrogenated stream obtained from (v-01) or the bottoms    stream obtained from (v-02) is subjected to further work-up as    stream S1. If steps (v-01) and/or (v-02) is/are carried out, it is    preferred-   (v-01) to subject the stream SO2 obtained from (v) to a catalytical    hydrogenation stage, the catalyst preferably being a heterogeneous    catalysts comprising Ru, Ni, Pd, Pt, either individually or as a    mixture of two or more thereof, as active metal on a suitable    support material, in particular Pd on activated carbon; said    hydrogenation preferably being carried out at a pressure during    hydrogenation in the range of from 1 to 100 bar(abs), preferably    from 1 to 10 bar(abs), and a temperature during hydrogenation so in    the range of from 0 to 180° C., preferably from 25 to 120° C., more    preferably from 65 to 85° C.; and/or-   (v-02) to subject the stream obtained from (v) or from (v-01) to a    distillation stage, preferably carried out in a distillation column    operated at a top pressure of from 0.7 to 2 bar, more preferably of    from 1.1 to 2 bar.

Preferably, the process of the present invention neither comprises(v-01) nor (v-02).

Further Work-Up Steps

Preferably, in particular if the liquid feed stream provided in (i)comprises the at least one component B, the further work-up stages arecarried out by a process whose preferred steps and conditions aredefined by the following embodiments 1 to 13 and the respectivecombinations of embodiments resulting from the dependencies asindicated:

-   1. (vi) dividing S1 into two streams S2 and S3, wherein the total    weight of S3 relative to the total weight of S1 is in the range of    from 0.01 to 25%;    -   (vii) subjecting S3 to a vapor-liquid fractionation in a        fractionation unit, obtaining a vapor fraction stream S4 being        depleted of the at least one component B, and obtaining a liquid        bottoms stream S4b being depleted of acetonitrile:    -   (viii) recycling at least a portion of S4, optionally after        work-up, to (i).-   2. The process of embodiment 1, wherein in (vi), the total weight of    S3 relative to the total weight of S1 is in the range of from 0.05    to 20%, preferably from 0.1 to 15%, more preferably from 0.2 to 10%,    more preferably from 0.5 to 5%.-   3. The process of embodiment 1 or 2, wherein from 90 to 99.9    weight-%, preferably from 95 to 99.8 weight-%, more preferably from    99 to 99.7 weight-% of S1 consist of acetonitrile and water and    wherein preferably from 0.01 to 5 weight-%, more preferably from    0.015 to 3 weight-%, more preferably from 0.02 to 2 weight-% of S1    consist of the at least one component B.-   4. The process of any of embodiments 1 to 3, wherein in (vii),    vapor-liquid fractionation is carried out in the fractionation unit    so that from 10 to 30 weight-%, preferably from 10 to 25 weight-% of    the liquid bottoms stream S4b consist of acetonitrile and from 0.1    to 10 weight-%, preferably from 0.25 to 5 weight-% of the liquid    bottoms stream S4b consist of the at least one further component B.-   5. The process of any of embodiments 1 to 4, wherein in (vii),    vapor-liquid fractionation is carried out in the fractionation unit    at an absolute pressure in the range of from 0.1 to 10 bar,    preferably from 0.5 to 5 bar, more preferably from 1 to 2 bar.-   6. The process of any of embodiments 1 to 5, wherein in (vii), the    number of theoretical trays of the fractionation unit is in the    range of from 1 to 100, preferably from 2 to 25, more preferably    from 3 to 10.-   7. The process of any of embodiments 1 to 6, wherein a fraction of    S4 is used after condensation as reflux, the reflux ratio preferably    being in the range of from 0.01:1 to 10:1, more preferably from    0.1:1 to 5:1, more preferably from 0.5:1 to 2:1.-   8. The process of any of embodiments 1 to 6, wherein the    fractionation unit is operated without reflux and S3 is fed to the    top of the fractionation unit.-   9. The process of any of embodiments 1 to 8, wherein from 95 to    99.99 weight-%, preferably from 97 to 99.9 weight-%, more preferably    from 98 to 99.9 weight-% of S4 consist of acetonitrile and water,    and wherein preferably from 0.0001 to 0.2 weight-%, more preferably    from 0.001 to 0.15 weight-%, more preferably from 0.005 to 0.1    weight-% of S4 consist of the at least one component B.-   10. The process of any of embodiments 1 to 9, wherein (viii)    comprises recycling at least a portion of S4, optionally after    work-up, to (i), and recycling at least a portion of S2, optionally    after work-up, to step (i).

According to the present invention, the effluent stream removedaccording to (iii) comprises at least a portion of the at least onepotassium salt comprised in the feed stream provided in (i). Preferably,the propylene oxide is separated from the effluent stream in one or moresuitable stages described hereinabove. Further preferably, the thusobtained stream depleted of propylene oxide is subjected to one or morefurther stages from which an acetonitrile recycle stream is preferablyobtained which is fed back to the epoxidation reaction. A preferredrecycling method comprising a stage (viii) is described hereinabove.Preferably, at least a portion of the at least one potassium saltcomprised in the effluent stream according to (iii) and preferablycomprised in the stream S4, more preferably in the streams S4 and S2, issuitably separated from the recycle stream(s) during work-up of S2and/or S4. More preferably, at least 99%, preferably at least 99.9% morepreferably at least 99.99% of the at least one potassium salt comprisedin S4, preferably comprised in the streams S4 and S2, are separated fromthe recycle stream(s) during work-up of S2 and/or S4. Therefore, it isespecially preferred that an accumulation of the at least one potassiumsalt caused by a re-use of the recycle stream(s) in (i) is essentiallycompletely prevented.

The Catalytic System

According to the present invention, it was found that the specificcombination of a titanium zeolite of framework structure type MWW whichoptionally comprises zinc, and at least one potassium salt which isemployed as additive leads to unexpected and superior characteristics ofthe epoxidation reaction where propylene oxide is prepared from propene,preferably with hydrogen peroxide as epoxidation agent, and preferablyin the presence of acetonitrile as solvent. Therefore, the presentinvention also relates to a catalytic system comprising a catalystcomprising a titanium zeolite of structure type MWW optionallycomprising zinc, and at least one potassium salt. The term “catalyticsystem” as used in this context of the present invention relates to thesystem comprised of catalyst comprising a titanium zeolite of structuretype MWW optionally comprising zinc, and the at least one potassium saltwhich catalytic system is realized when the liquid feed provided in (i)is brought in contact with the catalyst in (ii). This catalytic systemis characterized by the following embodiments and combinations ofembodiments resulting from the dependencies as indicated:

-   1. A catalytic system comprising a catalyst comprising a titanium    zeolite of structure type MWW optionally comprising zinc, preferably    comprising a titanium zeolite of framework structure type MWW    comprising zinc, and at least one potassium salt.-   2. The catalytic system of embodiment 1, wherein the at least one    potassium salt is selected from the group consisting of at least one    inorganic potassium salt, at least one organic potassium salt, and a    combination of at least one inorganic potassium salt and at least    one organic potassium salt.-   3. The catalytic system of embodiment 1 or 2, wherein the at least    one potassium salt is selected from the group consisting of at least    one inorganic potassium salt selected from the group consisting of    potassium hydroxide, potassium halides, potassium nitrate, potassium    sulfate, potassium hydrogen sulfate, potassium perchlorate, at least    one organic potassium salt selected from the group consisting of    potassium salts of aliphatic saturated monocarboxylic acids    preferably having 1, 2, 3, 4, 5 or 6 carbon atoms, potassium    carbonate, and potassium hydrogen carbonate, and a combination of at    least one of the at least one inorganic potassium salts and at least    one of the at least one organic potassium salts.-   4. The catalytic system of any of embodiments 1 to 3, wherein the at    least one potassium salt is selected from the group consisting of    potassium hydroxide, potassium chloride, potassium nitrate, at least    one organic potassium salt selected from the group consisting of    potassium formate, potassium acetate, potassium carbonate, and    potassium hydrogen carbonate, and a combination of at least one of    the at least one inorganic potassium salts and at least one of the    at least one organic potassium salts-   5. The catalytic system of any of embodiments 1 to 4, wherein the at    least one potassium salt comprises potassium formate, potassium    acetate, or a mixture thereof, preferably potassium formate.-   6. The catalytic system of any of embodiments 1 to 5, wherein the    titanium zeolite of structure type MWW optionally comprising zinc    which is comprised in the catalyst contains titanium, calculated as    elemental titanium, in an amount in the range of from 0.1 to 5    weight-%, preferably from 1 to 2 weight-%, based on the total weight    of the titanium zeolite of framework structure type MWW optionally    comprising zinc, and optionally contains zinc, calculated as    elemental zinc, in an amount in the range of from 0.1 to 5 weight-%,    preferably from 1 to 2 weight-%, based on the total weight of the    titanium zeolite of framework structure type MWW optionally    comprising zinc.-   7. The catalytic system of any of embodiments 1 to 6, wherein the    catalyst comprising a titanium zeolite of framework structure type    MWW optionally comprising zinc is a fixed-bed catalyst.-   8. The catalytic system of any of embodiments 1 to 7, wherein the    catalyst comprising a titanium zeolite of framework structure type    MWW comprises zinc and is in the form of a molding, the molding    being characterized by the following embodiments and combination of    embodiments resulting from the dependencies as indicated:    -   8.1 A molding, comprising a microporous aluminum-free zeolitic        material of structure type MWW containing titanium and zinc        (ZnTiMWW), said molding preferably comprising a micropowder        comprising, based on the weight of the micropowder, at least 95        weight-% of a microporous aluminum-free zeolitic material of        structure type MWW containing titanium and zinc (ZnTiMWW), said        molding more preferably comprising the micropowder according to        any of the micropowder embodiments 1 to 14 as described        hereinabove, the molding preferably further comprising at least        one binder, preferably a silica binder.    -   8.2 The molding of embodiment 8.1, comprising mesopores having        an average pore diameter in the range of from 4 to 40 nm,        preferably from 20 to 30 nm as determined by Hg porosimetry        according to DIN 66133.    -   8.3 The molding of embodiment 4.1 or 4.2, having a        crystallinity, as determined by XRD analysis, of at least (55        +/−10) %, preferably in the range of from ((55 to 75) +/−10) %.        The crystallinity is understood as being determined according to        Reference Example 4.7 of the present invention.    -   8.4 The molding of any of embodiments 8.1 to 8.3, comprising the        micropowder in an amount in the range of from 70 to 80 weight-%        and the silica binder in an amount of from 30 to 20 weight-%,        the micropowder together with the silica binder constituting at        least 99 weight-% of the molding, wherein the molding has a        concentration of silanol groups with respect to the total number        of Si atoms of at most 6%, preferably at most 3%, as determined        according to ²⁹Si MAS NMR. The concentration of the silanol        groups is understood as being determined according to Reference        Example 4.2 of the present invention.    -   8.5 The molding of any of embodiments 8.1 to 8.4, being a strand        having circular cross-section and a diameter in the range of        from 1.5 to 1.7 mm and having a crush strength of at least 5 N,        preferably in the range of from 5 to 20 N, more preferably in        the range of from 12 to 20 N, the crush strength being        determined by crush strength test machine Z2.5/TS1S according to        the method as described in Reference Example 4.3 of the present        invention.    -   8.6 The molding of any of embodiments 8.1 to 8.5, the ²⁹Si-NMR        spectrum of said molding comprising six peaks at the following        position    -   peak 1 at −98+/−x ppm,    -   peak 2 at −104+/−x ppm,    -   peak 3 at −110+/−x ppm,    -   peak 4 at −113+/−x ppm,    -   peak 5 at −115+/−x ppm,    -   peak 6 at −118+/−x ppm,    -   with x in any of the peaks being 1.5, preferably 1.0, more        preferably 0.5,    -   wherein Q which is defined as        Q=100*{[a ₁ +a ₂ ]/[a ₄ +a ₅ +a ₆ ]}/a ₃    -   is at most 2.5, preferably at most 1.6, preferably at most 1.4,        with [a₁+a₂] being the sum of the peak areas of peaks 1 and 2,        and [a₄ +a₅ +a₆] being the sum of the peak areas of peaks 4, 5,        and 6, and a₃ being the peak area of peak 3. These ²⁹Si-NMR        characteristics are understood as being determined according the        Reference Example 4.4 of the present invention.    -   8.7 The molding of any of embodiments 8.1 to 8.6, having a water        uptake in the range of from 3 to 8 weight-%, preferably from 4        to 7 weight-%. The water uptake is understood as being        determined according to Reference Example 4.5 of the present        invention.    -   8.8 The molding of any of embodiments 8.1 to 8.7, the infrared        spectrum of said molding comprising a band in the region of        (3700-3750) +/−20 cm⁻¹ and a band in the region of (3670-3690)        +/−20 cm⁻¹, wherein the intensity ratio of the band in the        region of (3700-3750) +/−20 cm⁻¹ relative to the band in the        region of (3670-3690) +/−20 cm⁻¹ is at most 1.5, preferably at        most 1.4.-   9. The catalytic system of any of embodiments 1 to 8 for the    epoxidation of propene.-   10. The catalytic system of any of embodiments 1 to 9, being    obtainable or obtained by    -   (i′) providing a liquid feed stream comprising propene, hydrogen        peroxide, acetonitrile, water, optionally propane, the at least        one dissolved potassium salt, wherein in (i′), the molar ratio        of potassium relative to hydrogen peroxide in the liquid feed        stream is preferably in the range of from 25×10⁻⁶:1 to        1000×10⁻⁶:1, more preferably from 50×10⁻⁶:1 to 250×10⁻⁶:1, more        preferably from 100×10⁻⁶:1 to 150×10⁻⁶:1;    -   (ii′) passing the liquid feed stream provided in (i′) into an        epoxidation reactor comprising the catalyst comprising a        titanium zeolite of structure type MWW optionally comprising        zinc, wherein in (ii′), the liquid feed stream is preferably        subjected to epoxidation reaction conditions in the epoxidation        reactor, obtaining a reaction mixture comprising propylene        oxide, acetonitrile, water, the at least one, potassium salt,        optionally propene, and optionally propane.-   11. The catalytic system of embodiment 10, wherein the liquid feed    stream provided in (i′) comprises    -   the acetonitrile in amount of from 60 to 75 weight-%, preferably        from 60 to 65 weight-%, based on the total weight of the liquid        feed stream;    -   the hydrogen peroxide in an amount of from 6 to 10 weight-%,        preferably from 7 to 9 weight-%, based on the total weight of        the liquid feed stream;    -   the water in a molar ratio of water relative to acetonitrile of        at most 1:4, preferably in the range of from 1:50 to 1:4,        preferably from 1:15 to 1:4.1, more preferably from 1:10 to        1:4.2;    -   the propene with a molar ratio of propene relative to hydrogen        peroxide comprised in the liquid feed stream in the range of        from 1:1 to 1.5:1, preferably from 1.1:1 to 1.4:1;    -   the at least one dissolved potassium salt with a molar ratio of        potassium comprised in the at least one potassium salt relative        to hydrogen peroxide comprised in the liquid feed stream in the        range of from 5×10⁻⁶:1 to 1000×10⁻⁶:1, preferably from 25×10⁻⁶:1        to 500×10⁻⁶:1, more preferably from 50×10⁻⁶:1 to 250×10⁻⁶:1; and    -   optionally the propane with a molar ratio of propane relative to        the sum of propene and propane in the range of from 0,0001:1 to        0.15:1, preferably from 0.001:1 to 0.05:1; wherein preferably at        least 95 weight-%, more preferably from 95 to 100 weight-%,    -   more preferably from 98 to 100 weight-% of the liquid feed        stream provided in (i) consist of propene, hydrogen peroxide,        acetonitrile, water, the at least one potassium salt, and        optionally propane.-   12. The catalytic system of embodiment 10 or 11, wherein the liquid    feed stream provided in (i′) contains ammonium NH₄ ⁺ in amount of at    most 2 weight-ppm, preferably at most 1 weight-ppm.-   13. The catalytic system of any of embodiments 10 to 12, wherein the    liquid feed stream provided in (i′) contains sodium in a molar ratio    of sodium relative to hydrogen peroxide in the range of from    1×10⁻⁶:1 to 250×10⁻⁶:1, preferably from 5×10⁻⁶:1 to 50×10⁻⁶:1.-   14. The catalytic system of any of embodiments 10 to 13, wherein the    liquid feed stream passed into the reactor in (ii′) has a    temperature in the range of from 0 to 60° C., preferably from 25 to    50° C., and is at a pressure in the range of from 14 to 100 bar,    preferably from 15 to 25 bar.-   15. The catalytic system of any of embodiments 10 to 14, wherein in    (ii′), the temperature of the reaction mixture is controlled using a    heat transfer medium, preferably by passing the heat transfer medium    through a jacket of the epoxidation reactor.-   16. The catalytic system of any of embodiments 10 to 15, wherein in    (ii′), the epoxidation conditions comprise an epoxidation reaction    temperature in the range of from 20 to 100° C., preferably from 30    to 80° C., more preferably from 40 to 60° C., wherein the    epoxidation reaction temperature is defined as the temperature of    the heat transfer medium prior to controlling of the temperature of    the reaction mixture, preferably as the temperature of the heat    transfer medium at the entrance of the jacket of the epoxidation    reactor-   17. The catalytic system of any of embodiments 10 to 16, wherein in    (ii′), the epoxidation conditions comprise an epoxidation reaction    pressure in the range of from 14 to 100 bar, preferably from 15 to    32 bar, more preferably from 15 to 25 bar, wherein the epoxidation    reaction pressure is defined as the pressure at the exit of the    epoxidation reactor.-   18. The catalytic system of any of embodiments 10 to 17, wherein in    (ii′), the reaction mixture is liquid under the epoxidation    conditions, the reaction mixture preferably consisting of one single    liquid phase under the epoxidation conditions.

Yet further, the present invention relates to the use, or a method ofusing, of at least one potassium salt as an additive for a titaniumzeolite of framework structure type MWW optionally comprising zinc,preferably for a titanium zeolite of framework structure type MWWcomprising zinc, in a preferably continuous process for the preparationof propylene oxide, preferably in acetonitrile as solvent, andpreferably with hydrogen peroxide as epoxidation agent.

Preferably, the present invention relates to said use, or said method ofusing, wherein the at least one potassium salt is preferably selectedfrom the group consisting of at least one inorganic potassium saltselected from the group consisting of potassium hydroxide, potassiumhalides, potassium nitrate, potassium sulfate, potassium hydrogensulfate, potassium perchlorate, at least one organic potassium saltselected from the group consisting of potassium salts of aliphaticsaturated monocarboxylic acids preferably having 1, 2, 3, 4, 5 or 6carbon atoms, potassium carbonate, and potassium hydrogen carbonate, anda combination of at least one of the at least one inorganic potassiumsalts and at least one of the at least one organic potassium salts.

More preferably, the present invention relates to said use, or saidmethod of using, wherein the at least one potassium salt is selectedfrom the group consisting of at least one inorganic potassium saltselected from the group consisting of potassium hydroxide, potassiumhalides, potassium nitrate, potassium sulfate, potassium hydrogensulfate, potassium perchlorate, at least one organic potassium saltselected from the group consisting of potassium formate, potassiumacetate, potassium propionate, potassium carbonate, and potassiumhydrogen carbonate, and a combination of at least one of the at leastone inorganic potassium salts and at least one of the at least oneorganic potassium salts.

More preferably, the present invention relates to said use, or saidmethod of using, wherein the at least one potassium salt is selectedfrom the group consisting of at least one inorganic potassium saltselected from the group consisting of potassium hydroxide, potassiumchloride, potassium nitrate, at least one organic potassium saltselected from the group consisting of potassium formate, potassiumacetate, potassium carbonate, and potassium hydrogen carbonate, and acombination of at least one of the at least one inorganic potassiumsalts and at least one of the at least one organic potassium salts.

The present invention is further illustrated by the following referenceexamples, examples, and comparative examples.

EXAMPLES Reference Example 1 Epoxidation Reaction Setup

A vertically arranged tubular reactor (length: 1.4 m, internal diameter:7 mm) equipped with a jacket for thermostatization was charged with 15 gof ZnTiMWW catalyst in the form of strands with a diameter of 1.5 mm asdescribed in Reference Example 2 below. The remaining reactor volume wasfilled with inert material (steatite spheres, 2 mm in diameter) to aheight of about 5 cm at the lower end of the reactor and the remainderat the top end of the reactor.

The reactor was thermostatized by passing a mixture of water andethylene glycol as heat transfer medium through the jacket. The heattransfer medium was fed at the lower end of the jacket, flowing inco-current mode relative to the liquid feed stream passed into thereactor. The temperature of the heat transfer medium at the entrance ofthe jacket was defined as the reaction temperature, also referred to asT_(r). The flow rate of the heat transfer medium was suitably adjustedso that the difference between its temperature at the entrance of thejacket and its temperature at the exit of the jacket was at most 1 K.

The pressure in the reactor was controlled by a pressure control valveand maintained at a constant value of 20 bar_(abs).

The reactor feed stream was combined from three separate feed streamswhich were metered by using separate metering pumps:

-   -   The first stream consisted either of acetonitrile (Asahi Kasei,        chemical grade, acetonitrile content at least 99.9 weight-%,        water content less than 500 weight-ppm). This first stream was        employed having a flow rate of 68 g/h.    -   The second stream consisted of liquefied polymer grade propene,        having a propane content of 99.5 weight-%. This second stream        was employed having a flow rate of 10.8 g/h.    -   The third stream consisted of an aqueous hydrogen peroxide        solution with a hydrogen peroxide concentration of 40 weight-%.        This third stream was employed having a flow rate of 16.8 g/h.        Potassium salts used in the experiments as additives were        dissolved in the hydrogen peroxide stream in amounts shown below        in the Examples.

The three feed streams were premixed before the mixed feed was fed atambient temperature to the bottom of the tubular reactor as liquid feedstream. Under the conditions the liquid feed stream consisted of onesingle liquid phase.

The experiments were performed in a continuous manner. At the start ofthe run (t=0, defined as the point in time at which the hydrogenperoxide metering pump was started), the reaction temperature was set toa value in the range of 30 to 45° C. as shown in the examples. With afresh catalyst this resulted in an initial 100% conversion of hydrogenperoxide. After a certain period of time, usually within 100 hours onstream, the hydrogen peroxide conversion started to decrease. Thetemperature was then adjusted, generally once to twice a day, in orderto keep the hydrogen peroxide conversion in a range of from 85 to 96%.The average rate at which the temperature was increased in order to keepthe hydrogen peroxide conversion essentially constant, referred tohereinbelow as the parameter delta T_(r)/delta t, is a measure of therate of catalyst deactivation. This parameter was calculated by dividingthe difference between the cooling medium temperature at end of theindicated time period and the starting temperature and dividing it bythe total number of hours on stream.

The reactor effluent stream downstream the pressure control valve wascollected, weighed and analyzed. Organic components, with the exceptionof hydroperoxypropanols and oxygen were analyzed in two separategas-chromatographs. The hydrogen peroxide content was determinedcolorimetrically using the titanyl sulfate method. The content ofhydroperoxypropanols, a mixture of 1-hydroperoxypropanol-2 and2-hydroperoxypropanol-1, was determined by iodometrically measuring thetotal peroxide content and then subtracting the hydrogen peroxidecontent.

The selectivity for propylene oxide given was determined relative to thehydrogen peroxide and was calculated as 100 times the ratio of moles ofpropylene oxide in the effluent stream divided by the moles of hydrogenperoxide in the feed. The selectivity for propylene glycol given wascalculated as 100 times the ratio of moles of propylene glycol in theeffluent divided by the moles of hydrogen peroxide in the feed. Theselectivity for hydroperoxypropanols given was calculated as 100 timesthe ratio of twice the number of moles of hydroperoxypropanols in theeffluent divided by the moles of hydrogen peroxide in the feed. Theselectivity for molecular oxygen given was calculated as 100 times theratio of twice the number of moles of molecular oxygen in the effluentdivided by the moles of hydrogen peroxide in the feed.

Reference Example 2 Preparation of Epoxidation Reaction Catalyst(ZnTiMWW)

2.1 Preparation of Boron Containing Zeolite of Structure MWW (BMWW)

-   -   A 2 m³ stirred tank reactor was first loaded with 470.4 kg of        deionized water. After starting the stirrer at 70 rpm, boric        acid (162.5 kg) was added and the suspension was stirred for        3 h. Subsequently, piperidine (272.5 kg) was added at once        causing the temperature to rise from 28° C. to 46° C. To this        solution colloidal silica (Ludox AS40, 392.0 kg) was added. The        reactor was then slowly heated to 170° C. within 5 hours and        then kept at this temperature under stirring for 120 hours. The        maximum pressure during the reaction was 9.3 bar. Afterwards the        reactor was cooled down to 50° C. The gel obtained had a pH of        11.3 and a viscosity of 15 mPa·s at 20° C. The gel was then        filtered and the filter cake washed with deionized water until        the conductivity of the washings was below 500 microSiemens/cm.        The filter cake was then suspended in deionized water and the        suspension was spray-dried at 235° C. using nitrogen as the        carrier gas. The white powder obtained (174.3 kg) contained 3.5        weight-% water. This white powder was then calcined at 650° C.        in a rotary kiln to give 138.2 kg of boron containing zeolite of        structure type MWW (BMWW) as a white powder.        2.2 Deboronation of BMWW with Water    -   A 5 m³ stirred tank reactor was loaded with 125 kg of the BMWW        obtained according to the previous step and 3750 kg of deionized        water. The reactor was then slowly heated to 100° C. within 1        hour under stirring at 70 rpm, and then kept at this temperature        for 20 hours and finally cooled to a temperature below 50° C.        before it was filtered. The filter cake was then washed with        deionized water until the washings had conductivity below 15        microSiemens. The filter cake was then dried for 6 hours under a        nitrogen stream. The filter cake was then removed and suspended        in 850 kg of deionized water. This suspension was then        spray-dried at 235° C. using nitrogen as the carrier gas. The        spray dried material weighed 118.5 kg and contained 42.5        weight-% Si, 0.06 weight-% B and 0.23 weight-% C (total organic        carbon, TOC).        2.3 Preparation of Titanium Containing Zeolite of Structure Type        MWW (TiMWW)    -   A 2 m³ stirred tank reactor was first loaded with 111.2 kg of        the spray-dried material from the previous step 2.2. In a        separate 2 m³ stirred tank reactor were placed 400 kg of        deionized water. After starting the stirrer at 80 rpm,        piperidine (244.0 kg) was added. After the addition of        piperidine was finished the mixture was stirred for 5 minutes        before tetrabutyl orthotitanate (22.4 kg) was added. The pipe        through which the titanate was added was then flushed with 40 kg        of deionized water. The mixture was then stirred for 1 hour        before being added to the first stirred tank reactor containing        the spray-dried powder under stirring (50 rpm). The reactor was        then heated to 170° C. and kept at this temperature for 120 h        before being cooled to 50° C. The maximum pressure during the        reaction was 10.6 bar. The cooled suspension was then filtered        and the filter cake was washed with deionized water until the        washings had conductivity below 1300 microSiemens/cm and an        approximately neutral pH value. The filter cake was then dried        under a nitrogen stream for 6 hours. The filter cake containing        about 80 weight-% of water was used directly for the next step.        The filter cake from the previous step and 1000 kg of deionized        water were filled in a 2 m³ stirred tank reactor. Then 1900 kg        of nitric acid (53 weight-% in water) were added under stirring        at 70 rpm. The reactor was then heated to 100° C. and kept at        this temperature for 20 hours before being cooled to 50° C. The        suspension obtained was then filtered and the filter cake was        washed with deionized water until the conductivity was below 10        microSiemens/cm and the washings were approximately neutral.        Subsequently the filter cake was dried under a stream of        nitrogen for 6 hours. This filter cake was then suspended in        water and spray-dried at 235° C. using nitrogen as the carrier        gas. 96 kg of a spray-dried powder were obtained. This material        was then calcined in a rotary kiln at 650° C. 84 kg of titanium        zeolite of structure type MWW (TiMWW) were obtained as a powder        containing 43 weight-% Si, 2.0 weight-% Ti and 0.2 weight-% C        (TOC). The pore volume determined by Hg-porosimetry according to        DIN 66133 was 7.3 ml/g and the BET surface area determined        according to DIN 66131 was 467 m²/g.        2.4 Preparation of a Zinc Containing TiMWW (ZnTiMWW) by        Impregnation    -   A 2 m³ stirred tank reactor was then loaded with 960 kg of water        and 5.83 kg of zinc acetate dihydrate. After stirring for 30        min, TiMWW powder (32.0 kg, obtained according to the previous        step) was added. The reactor was then heated to 100° C. and kept        at this temperature for 4 hours before being cooled to 50° C.        The suspension obtained was then filtered and the filter cake        was washed 5 times with 120 liter portions of deionized water.        The washed filter cake was then dried under a stream of nitrogen        for 6 hours. It was then suspended in deionized water and        spray-dried at 235° C. using nitrogen as the carrier gas. 34 kg        of spray-dried material were obtained which was then calcined at        650° C. for 30 min in a rotary kiln. 28.5 kg of TiMWW containing        zinc (ZnTiMWW) powder were obtained that contained 42 weight-%        Si, 1.9 weight-% Ti, 1.6 weight-% Zn and 0.16 weight-% C (TOC).        The pore volume determined by Hg-porosimetry according to DIN        66133 was 6.6 ml/g and the BET surface area determined according        to DIN 66131 was 335 m²/g.        2.5 Preparation of Moldings Containing ZnTiMWW and Silica Binder    -   In a kneader the ZnTiMWW powder from the previous step (27.0 kg)        and hydroxymethylcellulose (Walocel™, 2.0 kg) were kneaded for 5        minutes. Then colloidal silica (Ludox® AS 40, 16.9 kg) was        added. After kneading for 10 minutes deionized water (57.6 kg)        was added and the mixture was kneaded for further 60 minutes.        The paste obtained was then extruded through plates with        cylindrical holed with 1.5 mm diameter with a pressure of 65-80        bar. The strands obtained were dried for 16 hours at 120° C. and        then calcined for 5 hours at 500° C. The strands obtained were        then sieved in a 0.8 mm sieve to remove fines. The ZnTiMWW        catalyst strands obtained (34.2 kg) had a diameter of 1.5 mm and        lengths between 5 and 25 mm. The bulk density of the catalyst        was 345 g/l. The pore volume determined by Hg-porosimetry        determined according to DIN 66133 was 1.1 ml/g and the BET        surface area determined according to DIN 66131was 371 m²/g. The        elementary analysis showed that the molded ZnTiMWW catalyst        contained 41 weight-% Si, 1.4 weight-% Ti and 1.2 weight-% Zn.

Reference Example 3 Preparation of Epoxidation Reaction Catalyst (TiMWW)

3.1 Preparation of Boron Containing Zeolite of Structure MWW (BMWW)

-   -   A 50 liter stirred tank reactor was loaded with 22.05 kg of        deionized water and 8.515 kg of piperidine. The mixture was then        stirred for a few minutes at 150 rpm before 5.076 kg of boric        acid were added. The resulting mixture was stirred for 30        minutes. Pyrogenic silica (Aerosil 200, 4.9 kg) was then added        portion wise and the resulting suspension was stirred for 2        hours. The reactor was then heated to 170° C. within 2 hours and        kept at this temperature for 120 hours. The maximum pressure        during the reaction was 8.9 bar. After cooling to 50° C. the        suspension was filtered and the filter cake was washed twice,        each washing using 50 liters of deionized water. The filter cake        was then dried for 24 hours at 80° C. under a stream of        nitrogen, then oven-dried at 100° C. for 16 hours and finally        calcined at 600° C. for 10 hours to obtain 4.95 kg of a white        BMWW powder containing 1.4 weight-% B.        3.2 Deboronation of BMWW with Acid    -   A 200 liter stirred tank reactor was loaded with 150 kg of        nitric acid (30 weight-% in water) and the BMWW powder from the        previous step and stirred at 100 rpm for 10 minutes. The reactor        was then heated to 100° C. and kept at this temperature under        stirring for 20 hours. After cooling to 50° C. the suspension        was filtered and the filter cake washed with deionized water        until the washings were approximately neutral. The filter cake        was then dried for 15 hours under a stream of nitrogen and        finally oven dried at 120° C. for 16 hours. 4.117 kg of a white        powder containing 0.061 weight-% B were obtained.        3.3 Preparation of Titanium Containing Zeolite of Structure Type        MWW (TiMWW)    -   A 20 liter stirred tank reactor was then loaded with 10.5 kg of        deionized water and 5.07 kg of piperidine. The mixture was        stirred (170 rpm) for 10 minutes before adding 700 g of        tetrabutyl orthotitanate. The mixture was stirred for a further        30 min and then 3.5 kg of the powder obtained from the previous        step 3.2 were added. After stirring for 2 hours the reactors was        heated to 170° C. and kept at this temperature for 120 hours.        The maximum pressure during the reaction was 9.1 bar. After        cooling to 50° C. the resulting suspension was filtered and the        filter cake was washed with twice with 25 liters of deionized        water per washing. The filter cake was then dried at 100° C. for        48 hours. 4.073 kg of a wet white powder containing 2.3 weight-%        Ti, 36.0 weight-% Si and 10.4 weight-% C (TOC) were obtained.        The powder (4.0 kg) and 120 kg of nitric acid (30 weight-% in        water) were then loaded to a 200 liter stirred tank reactor. The        suspension was then stirred at 100 rpm and the reactor heated to        100° C. and kept at this temperature for 20 hours. After cooling        to 50° C. the resulting suspension was filtered and the filter        cake washed with deionized water until the washings were        approximately neutral. The filter cake was then dried at 120° C.        for 16 hours and finally calcined at 550° C. for 10 hours. 3.185        kg of TiMWW powder with 1.7 weight-% Ti and 45.0 weight-% Si        were obtained.        3.4 Preparation of Moldings Containing TiMWW and Silica Binder    -   TiMWW powder (3.0 kg) obtained from the previous step 3.3 and        hydroxymethylcellulose (Walocel™, 200 g) were kneaded for 5        minutes. Then colloidal silica (Ludox® AS40, 2.5 kg) were added        under continuous kneading. After a further 10 min of kneading        deionized water (3.0 kg) was added under kneading. The paste        thus obtained was then extruded through plates with cylindrical        holed with 1.5 mm diameter with a pressure of 75-85 bar. The        strands obtained were dried for 16 hours at 120° C. and then        calcined for 5 hours at 500° C. The strands obtained were then        sieved using a 0.8 mm sieve to remove fines. The TiMWW catalyst        strands obtained (3.88 kg) had a diameter of 1.5 mm and lengths        between 5 and 25 mm. The pore volume determined by        Hg-porosimetry according to DIN 66133 was 0.7 ml/g and the BET        surface area determined according to DIN 66131 was 92 m²/g. The        elementary analysis showed that the molded TiMVVW catalyst        contained 43.5 weight-% Si and 1.1 weight-% Ti.

Reference Example 4 Characterization of the Catalyst Reference Example4.1 Determination of Dv10, Dv50, and Dv90 Values

1.0 g of the micropowder is suspended in 100 g deionized water andstirred for 1 min. The sample was subjected to the measurement in anapparatus using the following parameters: Mastersizer S long bed version2.15, ser. No. 33544-325; supplier: Malvern Instruments GmbH,Herrenberg, Germany: focal width 300RF mm; beam length 10.00 mm; moduleMS17; shadowing 16.9%; dispersion model 3$$D; analysis modelpolydisperse correction none.

Reference Example 4.2 Determination of the Silanol Concentration of theMoldings of the Present Invention

For the determination of the silanol concentration, the ²⁹Si MAS NMRexperiments were carried out at room temperature on a VARIANInfinityplus-400 spectrometer using 5.0 mm ZrO₂ rotors. The ²⁹Si MAS NMRspectra were collected at 79.5 MHz using a 1.9 μs π/4 (microsecond pi/4)pulse with 10 s recycle delay and 4000 scans. All ²⁹Si spectra wererecorded on samples spun at 6 kHz, and chemical shifts were referencedto 4,4-dimethyl-4-silapentane sulfonate sodium (DSS). For thedetermination of the silanol group concentration, a given ²⁹Si MAS NMRspectrum is deconvolved by the proper Gaussian-Lorentzian line shapes.The concentration of the silanol groups with respect to the total numberof Si atoms is obtained by integrating the deconvolved ²⁹Si MAS NMRspectra.

Reference Example 4.3 Determination of the Crush Strength of theMoldings

The crush strength as referred to in the context of the presentinvention is to be understood as determined via a crush strength testmachine Z2.5/TS1S, supplier Zwick GmbH & Co., D-89079 Ulm, Germany. Asto fundamentals of this machine and its operation, reference is made tothe respective instructions handbook “Register 1:Betriebsanleitung/Sicherheitshandbuch für die Material-PrüfmaschineZ2.5/TS1S ”, version 1.5, December 2001 by Zwick GmbH & Co. TechnischeDokumentation, August-Nagel-Strasse 11, D-89079 Ulm, Germany. With saidmachine, a given strand is subjected to an increasing force via aplunger having a diameter of 3 mm until the strand is crushed. The forceat which the strand crushes is referred to as the crushing strength ofthe strand. The machine is equipped with a fixed horizontal table onwhich the strand is positioned. A plunger which is freely movable invertical direction actuates the strand against the fixed table. Theapparatus was operated with a preliminary force of 0.5 N, a shear rateunder preliminary force of 10 mm/min and a subsequent testing rate of1.6 mm/min. The vertically movable plunger was connected to a load cellfor force pick-up and, during the measurement, moved toward the fixedturntable on which the molding (strand) to be investigated ispositioned, thus actuating the strand against the table. The plunger wasapplied to the stands perpendicularly to their longitudinal axis.Controlling the experiment was carried out by means of a computer whichregistered and evaluated the results of the measurements. The valuesobtained are the mean value of the measurements for 10 strands in eachcase.

Reference Example 4.4 ²⁹Si Solid-state NMR Spectra Regarding Q³ and Q⁴Structures

The effect of the inventive water treatment on the molding related to Q³and Q⁴ structures in the material was characterized by comparing thechanges in ²⁹Si solid-state NMR spectra under comparable conditions. All²⁹Si solid-state NMR experiments were performed using a Bruker Advancespectrometer with 300 MHz ¹H Larmor frequency (Bruker Biospin, Germany).Samples were packed in 7 mm ZrO₂ rotors, and measured under 5 kHz MagicAngle Spinning at room temperature. ²⁹Si direct polarization spectrawere obtained using (pi/2)-pulse excitation with 5 microsecond pulsewidth, a ²⁹Si carrier frequency corresponding to −65 ppm in thespectrum, and a scan recycle delay of 120 s. Signal was acquired for 25ms under 45 kHz high-power proton decoupling, and accumulated over 10 to17 hours. Spectra were processed using Bruker Topspin with 30 Hzexponential line broadening, manual phasing, and manual baselinecorrection over the full spectrum width. Spectra were referenced withthe polymer Q8M8 as an external secondary standard, setting theresonance of the trimethylsilyl M group to 12.5 ppm. The spectra werethen fitted with a set of Gaussian line shapes, according to the numberof discernable resonances. Relating to the presently 5 assessed spectra,6 lines in total were used, accounting for the five distinct peak maxima(at approximately −118, −115, −113, −110 and −104 ppm) plus the clearlyvisible shoulder at −98 ppm. Fitting was performed using DMFit (Massiotet al., Magnetic Resonance in Chemistry, 40 (2002) pp 70-76). Peaks weremanually set at the visible peak maxima or shoulder. Both peak positionand line width were then left unrestrained, i.e., fit peaks were notfixed at a certain position. The fitting outcome was numerically stable,i.e., distortions in the initial fit setup as described above did leadto similar results. The fitted peak areas were further used normalizedas done by DMFit. After the water treatment of the invention, a decreaseof signal intensity at the left hand side of the spectrum was observed,a region that includes Q³ silanol structures (here especially: aroundand above −104 ppm, i.e. “left” of −104 ppm). Further, an increase ofsignal at the right hand side of the spectrum (here: below −110 ppm,i.e. “right” of −110 ppm) was observed, which region comprises Q⁴structures exclusively. For the quantification of spectrum changes, aratio was calculated that reflects changes in the peak areas “left hand”and “right hand”, as follows. The six peaks were labeled with 1, 2, 3,4, 5, and 6, and the ratio Q was calculated with the formula100*{[a₁+a₂]/[a₄+a₅+a₆]}/a₃. In this formula, a_(i, i=1 . . . 6)represents the area of the fitted peak to which this number wasattributed.

Reference Example 4.5 Water Adsorption/Desorption—Water Uptake

The water adsorption/desorption isotherms measurements were performed ona VTI SA instrument from TA Instruments following a step-isothermprogram. The experiment consisted of a run or a series of runs performedon a sample material that has been placed on the microbalance pan insideof the instrument. Before the measurement were started, the residualmoisture of the sample was removed by heating the sample to 100° C.(heating ramp of 5° C./min) and holding it for 6 h under a N₂ flow.After the drying program, the temperature in the cell was decreased to25° C. and kept isothermal during the measurements. The microbalance wascalibrated, and the weight of the dried sample was balanced (maximummass deviation 0.01 wt. %). Water uptake by the sample was measured asthe increase in weight over that of the dry sample. First, an adsorptioncurve was measured by increasing the relative humidity (RH) (expressedas weight-% water in the atmosphere inside of the cell) to which thesamples was exposed and measuring the water uptake by the sample atequilibrium. The RH was increased with a step of 10 wt. % from 5 to 85%and at each step the system controlled the RH and monitored the sampleweight until reaching the equilibrium conditions and recording theweight uptake. The total adsorbed water amount by the sample was takenafter the sample was exposed to the 85 weight-% RH. During thedesorption measurement the RH was decreased from 85 wt. % to 5 wt. %with a step of 10% and the change in the weight of the sample (wateruptake) was monitored and recorded.

Reference Example 4.6 FT-IR Measurements

The FT-IR (Fourier-Transformed-Infrared) measurements were performed ona Nicolet 6700 spectrometer. The molding was powdered and then pressedinto a self-supporting pellet without the use of any additives. Thepellet was introduced into a high vacuum (HV) cell placed into the FT-IRinstrument. Prior to the measurement the sample was pretreated in highvacuum (10⁻⁵ mbar) for 3 h at 300° C. The spectra were collected aftercooling the cell to 50° C. The spectra were recorded in the range of4000 to 800 cm⁻¹ at a resolution of 2 cm⁻¹. The obtained spectra arerepresented in a plot having on the x axis the wavenumber (cm⁻¹) and onthe y axis the absorbance (arbitrary units, a.u.). For the quantitativedetermination of the peak heights and the ratio between these peaks abaseline correction was carried out. Changes in the 3000-3900 cm⁻¹region were analyzed and for comparing multiple samples, as referencethe band at 1880±5 cm⁻¹ was taken.

Reference Example 4.7 Determination of Crystallinity Via XRD

The crystallinity of the zeolitic materials according to the presentinvention were determined by XRD analysis. The data were collected usinga standard Bragg-Brentano diffractometer with a Cu-X-ray source and anenergy dispersive point detector. The angular range of 2° to 70° (2theta) was scanned with a step size of 0.02°, while the variabledivergence slit was set to a constant illuminated sample length of 20mm.

The data were then analyzed using TOPAS V4 software, wherein the sharpdiffraction peaks were modeled using a Pawley fit containing a unit cellwith the following starting parameters: a=14.4 Angstrom (1Angstrom=10⁻¹⁰m) and c=25.2 Angstrom in the space group P6/mm. Thesewere refined to fit the data. Independent peaks were inserted at thefollowing positions. 8.4°, 22.4°, 28.2° and 43°. These were used todescribe the amorphous content. The crystalline content describes theintensity of the crystalline signal to the total scattered intensity.Included in the mod& were also a linear background, Lorentz andpolarization corrections, lattice parameters, space group andcrystallite size.

Reference Example 5 Definition and Determination of the Octanol-waterPartition Coefficient K_(OW)

The octanol-water partition coefficient K_(OW) of a given compound isdefined as the ratio of said compound's chemical concentration in theoctanol phase relative to said compound's chemical concentration in theaqueous phase in a two-phase system of 1-octanol and water at atemperature of 25° C. The octanol-water partition coefficient K_(OW) ofa given compound is determined using the shake-flask method whichconsists of dissolving the compound in a volume of high-purity 1-octanoland deionized water (pre-mixed and calibrated for at least 24 h) andmeasuring the concentration of the compound in each the 1-octanol phaseand the water phase by a sufficiently exact method, preferably via UVNISspectroscopy. This method is described in the OECD Guideline for thetesting of chemicals, number 107, adopted on Jul. 27, 1995.

EXAMPLES Potassium Salts as Additives Example 1

In a first run, potassium dihydrogen phosphate was dissolved in thethird stream, the aqueous hydrogen peroxide solution described above inReference Example 1. The concentration of the potassium dihydrogenphosphate was chosen so that the molar ratio of potassium relative tothe hydrogen peroxide in the liquid feed stream was 130×10⁻⁶:1. Inparticular, the concentration of the potassium dihydrogen phosphate inthe liquid feed stream was 130 micromol per mol hydrogen peroxide. Theepoxdation reaction was carried out as described above in ReferenceExample 1.

After a certain time on stream the reaction was stopped. At this pointin time, the hydrogen peroxide conversion had reached a value of 90%.Since for this additive and this catalytic system, comprising a ZnTiMWWcatalyst and potassium dihydrogen phosphate, excellent propylene oxideselectivities were observed, this system was set as reference system forall other systems below.

Examples 2 to 6

Since the use of potassium dihydrogen phosphate as additive led to suchgood results, the following examples and comparative examples werecarried out by starting the continuous epoxidation reaction withpotassium dihydrogen phosphate as additive. Then, the reaction wascontinued until the hydrogen peroxide conversion reached a value of 90%.

At this point in time, the addition of potassium dihydrogen phosphatevia the third stream described in Reference Example 1 was stopped andother potassium salts were used instead as indicated in Table 1 below.

For every potassium salt used, the concentration of the salt was chosenso that the potassium concentration in the liquid feed stream passed tothe epoxidation reactor remained at the value of example 1 (molar ratioof potassium relative to the hydrogen peroxide in the liquid feed stream130×10⁻⁶:1).

For every system, the epoxidation reaction was continued until, after afirst deviation of the hydrogen peroxide conversion, this conversionreached the value of 90% again, i.e. the value at which the additive hadalready been changed from potassium dihydrogen phosphate to anotheradditive. At a point, when this value of 90% conversion could be keptconstant for 48 hours without changing the reaction parameters, theepoxidation reaction was stopped.

The deactivation rate was then determined as the difference in thereaction temperature (delta Tr) divided by the period of time (delta t).The difference in the reaction temperature is defined as the reactiontemperature at the end of the epoxidation reaction (i.e. the reactiontemperature at which the hydrogen peroxide conversion had reached thevalue of 90% and could be kept constant for another 48 hours without anyfurther parameter changes within the system after having replacedpotassium dihydrogen phosphate by the new additive) minus the reactiontemperature at the point in time where potassium dihydrogen phosphatehad been used as additive, the hydrogen conversion had reached the valueof 90% and potassium dihydrogen phosphate had been replaced. The periodof time (delta t) is defined by the time on stream from the change inadditive until the end of the epoxidation reaction, i.e. the period oftime during which the epoxidiation reaction was carried out in thepresence of the additive replacing potassium dihydrogen phosphate.

Example 2a

As shown in Table 1 below, potassium formate was found to be the mostpreferred additive among all potassium salts tested. Therefore, afurther run was carried out in the same manner as the run according toExample 2, with the difference that potassium formate was used asadditive from the very beginning of the epoxidation reaction. Thedeactivation rate was then determined as the difference in the reactiontemperature (delta Tr) divided by the period of time (delta t). Thedifference in the reaction temperature is defined as the reactiontemperature at the beginning of the epoxidation reaction (i.e. thereaction temperature at the beginning of the experiment was identical tothe ones used in Examples 1 to 6 and Comparatives Examples 1 to 3) minusthe reaction temperature at the point in time the hydrogen peroxideconversion had reached the value of 90% and could be kept constantwithout any further parameter changes for 48 h.

COMPARATIVE EXAMPLES Salts Other than Potassium Salts as Additve; NoAdditive Comparative Example 1

The Comparative Example 1 was carried out as Example 2. However, afterthe hydrogen peroxide conversion had reached a value of 90% withpotassium dihydrogen phosphate as additive, the addition of potassiumdihydrogen phosphate was stopped, and via the third stream described inReference Example 1, no additive was used anymore.

Comparative Examples 2 to 3

The Comparative Examples 2 and 3 were carried out as Example 2. However,after the hydrogen peroxide conversion had reached a value of 90% withpotassium dihydrogen phosphate as additive, the addition of potassiumdihydrogen phosphate was stopped, and via the third stream described inReference Example 1, the additives according to Table 1 below were usedinstead. Regarding Comparative Example 2, the concentration of NH₄H₂PO₄was identical to the concentration of KH₂PO₄ according to Example 1,i.e. 130 micromol per mol hydrogen peroxide. Regarding ComparativeExample 3, the concentration of NaH₂PO₄ was identical to theconcentration of KH₂PO₄ according to Example 1, i.e. 130 micromol permol hydrogen peroxide.

TABLE 1 Results of the Examples and the Comparative Examplesdeactivation catalytic rate/ propylene oxide example additive system K/dselectivity/% 1 KH₂PO₄ ZnTiMWW  0 ¹⁾ 98.8 KH₂PO₄ 2 HCOOK ZnTiMWW −1.1498.8 HCOOK 2a ²⁾ HCOOK ZnTiMWW −2.18 99.1 HCOOK 3 K₂CO₃ ZnTiMWW −0.6798.4 K₂CO₃ 4 KHCO₃ ZnTiMWW −0.48 98.7 KHCO₃ 5 KOH ZnTiMWW +0.13 98.4 KOH6 KCl ZnTiMWW +0.19 98.4 KCl comp. 1 — ZnTiMWW +1.23 97.1 comp. 2NH₄H₂PO₄ ZnTiMWW +0.83 97.8 NH₄H₂PO₄ comp. 3 NaH₂PO₄ ZnTiMWW +0.58 97.4NaH₂PO₄ ¹⁾ reference value ²⁾ no replacement of additive; the potassiumformate was used as additive from the very beginning of the epoxidationreactionResults

Compared to the epoxidation reactions where either no additive or anadditive other than a potassium salt was employed, all epoxidationreactions which were carried out with a potassium salt as additiveshowed higher propylene oxide selectivities at the same hydrogenperoxide selectivity of 90%. Reference is made to Table 1, showing thatin all comparative examples, the propylene oxide selectivity is below orsignificantly below 98% whereas in the Examples, all respective valuesare significantly above 98% and, for potassium formate as additive, evenabove 99%. Thus, these reactions where potassium salts were employed asadditives lead to a higher yield in propylene oxide as valuable product,and the selectivity with regard to undesired by-products orside-products is decreased.

Further, it was found that these higher propylene oxide selectivites atconstant hydrogen peroxide conversion can be realized at advantageousdeactivation rate. Compared to the epoxidation reaction with potassiumdihydrogen phosphate as additive, the deactivation rate at the end of arun where no potassium salt was employed was at least +0.58 K/d, i.e.significantly higher than the maximum value of +0.19 K/d obtained forreactions where potassium salts were employed as additives. In thiscontext, it is noted that a positive value indicates that compared topotassium dihydrogen phosphate, a respective additive leads to anincrease in reaction temperature which in turn means that more energyhas to be provided to realize a given hydrogen peroxide conversion.Therefore, a low positive value and in particular a negative value arepreferred.

Therefore, on particular the organic potassium salts, represented bypotassium formate, potassium carbonate and potassium hydrogen carbonatein the Examples, and the respective catalytic systems show excellentsuitability for the epoxidation reaction since they all lead to anegative relative deactivation rate and, at the same time, to very highpropylene oxide selectivities. Especially potassium formate was found tobe of particular suitability since this additive showed the lowestrelative deactivation rate and, at the same time, the highest propyleneselectivity.

CITED LITERATURE

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The invention claimed is:
 1. A catalytic system of a continuous processfor the preparation of propylene oxide, comprising: a titanium zeoliteof structure type MWW optionally comprising zinc; and a potassium saltdissolved in an aqueous acetonitrile mixture: wherein the potassium saltcomprises at least one selected from the group consisting of aninorganic potassium salt, and an organic potassium salt.
 2. Thecatalytic system according to claim 1, wherein the potassium saltcomprises an inorganic potassium salt which is selected from the groupconsisting of potassium hydroxide, potassium chloride and potassiumnitrate.
 3. The catalytic system of claim 1, wherein a content oftitanium, calculated as elemental titanium, is from 0.1 to 5 weight-%,based on the total weight of the titanium zeolite of framework structuretype MWW.
 4. A continuous process for the preparation of propyleneoxide, comprising: acetonitrile as solvent; hydrogen peroxide asepoxidation agent; and the catalytic system of claim
 1. 5. The catalyticsystem according to claim 1, wherein the potassium salt comprises anorganic potassium salt which is selected from the group consisting ofpotassium formate, potassium acetate, potassium carbonate, and potassiumhydrogen carbonate.
 6. The catalytic system of claim 1, wherein thetitanium zeolite of structure type MWW comprises zinc and a content ofthe zinc, calculated as elemental zinc, is from 0.1 to 5 weight-%, basedon the total weight of the titanium zeolite of framework structure typeMWW.